clang: Clobber all .o files after a clang roll.
clang: Clobber all .o files after a clang roll.

This has the advantage that after a bad clang roll, try slaves don't
have to be manually clobbered once the roll has been reverted. I also
no longer have to remember to pass --clobber to clang roll tryjobs.

It's a bit annoying that a clang roll now requires a full rebuild for
devs, but so do header changes in base/, and we no longer need to send
"please clobber your build directory" emails after reverting a bad clang
roll.

BUG=113653
TEST=`rm third_party/llvm-bulid/cr_build-revision; tools/clang/scripts/update.sh`
clobbers .o files with all build systems.

Review URL: https://chromiumcodereview.appspot.com/9378012

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@121503 0039d316-1c4b-4281-b951-d872f2087c98

mohamed--abdel-maksoud/chromium.src,anirudhSK/chromium,dednal/chromium.src,Jonekee/chromium.src,chuan9/chromium-crosswalk,jaruba/chromium.src,markYoungH/chromium.src,axinging/chromium-crosswalk,keishi/chromium,hgl888/chromium-crosswalk,Chilledheart/chromium,dednal/chromium.src,hgl888/chromium-crosswalk,fujunwei/chromium-crosswalk,fujunwei/chromium-crosswalk,crosswalk-project/chromium-crosswalk-efl,hujiajie/pa-chromium,mohamed--abdel-maksoud/chromium.src,krieger-od/nwjs_chromium.src,fujunwei/chromium-crosswalk,jaruba/chromium.src,ondra-novak/chromium.src,timopulkkinen/BubbleFish,ondra-novak/chromium.src,markYoungH/chromium.src,axinging/chromium-crosswalk,timopulkkinen/BubbleFish,chuan9/chromium-crosswalk,fujunwei/chromium-crosswalk,patrickm/chromium.src,Fireblend/chromium-crosswalk,pozdnyakov/chromium-crosswalk,Pluto-tv/chromium-crosswalk,zcbenz/cefode-chromium,jaruba/chromium.src,anirudhSK/chromium,robclark/chromium,nacl-webkit/chrome_deps,Jonekee/chromium.src,krieger-od/nwjs_chromium.src,Just-D/chromium-1,robclark/chromium,bright-sparks/chromium-spacewalk,Chilledheart/chromium,robclark/chromium,crosswalk-project/chromium-crosswalk-efl,Just-D/chromium-1,PeterWangIntel/chromium-crosswalk,rogerwang/chromium,fujunwei/chromium-crosswalk,Chilledheart/chromium,patrickm/chromium.src,Pluto-tv/chromium-crosswalk,zcbenz/cefode-chromium,mohamed--abdel-maksoud/chromium.src,robclark/chromium,mohamed--abdel-maksoud/chromium.src,Pluto-tv/chromium-crosswalk,Pluto-tv/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,junmin-zhu/chromium-rivertrail,hgl888/chromium-crosswalk,dushu1203/chromium.src,rogerwang/chromium,bright-sparks/chromium-spacewalk,Chilledheart/chromium,Jonekee/chromium.src,keishi/chromium,mogoweb/chromium-crosswalk,krieger-od/nwjs_chromium.src,chuan9/chromium-crosswalk,M4sse/chromium.src,keishi/chromium,robclark/chromium,bright-sparks/chromium-spacewalk,hgl888/chromium-crosswalk-efl,krieger-od/nwjs_chromium.src,jaruba/chromium.src,jaruba/chromium.src,dednal/chromium.src,junmin-zhu/chromium-rivertrail,junmin-zhu/chromium-rivertrail,crosswalk-project/chromium-crosswalk-efl,hgl888/chromium-crosswalk,littlstar/chromium.src,bright-sparks/chromium-spacewalk,chuan9/chromium-crosswalk,anirudhSK/chromium,crosswalk-project/chromium-crosswalk-efl,dednal/chromium.src,ondra-novak/chromium.src,Fireblend/chromium-crosswalk,Fireblend/chromium-crosswalk,junmin-zhu/chromium-rivertrail,TheTypoMaster/chromium-crosswalk,timopulkkinen/BubbleFish,mohamed--abdel-maksoud/chromium.src,dushu1203/chromium.src,dushu1203/chromium.src,anirudhSK/chromium,dednal/chromium.src,zcbenz/cefode-chromium,rogerwang/chromium,nacl-webkit/chrome_deps,hgl888/chromium-crosswalk-efl,hujiajie/pa-chromium,patrickm/chromium.src,patrickm/chromium.src,bright-sparks/chromium-spacewalk,mohamed--abdel-maksoud/chromium.src,Chilledheart/chromium,Jonekee/chromium.src,ChromiumWebApps/chromium,M4sse/chromium.src,nacl-webkit/chrome_deps,jaruba/chromium.src,Jonekee/chromium.src,anirudhSK/chromium,jaruba/chromium.src,anirudhSK/chromium,pozdnyakov/chromium-crosswalk,axinging/chromium-crosswalk,Pluto-tv/chromium-crosswalk,hujiajie/pa-chromium,littlstar/chromium.src,keishi/chromium,timopulkkinen/BubbleFish,keishi/chromium,M4sse/chromium.src,Fireblend/chromium-crosswalk,M4sse/chromium.src,zcbenz/cefode-chromium,hujiajie/pa-chromium,ondra-novak/chromium.src,rogerwang/chromium,anirudhSK/chromium,junmin-zhu/chromium-rivertrail,hujiajie/pa-chromium,ChromiumWebApps/chromium,Fireblend/chromium-crosswalk,hujiajie/pa-chromium,pozdnyakov/chromium-crosswalk,junmin-zhu/chromium-rivertrail,chuan9/chromium-crosswalk,hgl888/chromium-crosswalk,ChromiumWebApps/chromium,mogoweb/chromium-crosswalk,dushu1203/chromium.src,M4sse/chromium.src,dushu1203/chromium.src,crosswalk-project/chromium-crosswalk-efl,Just-D/chromium-1,Chilledheart/chromium,hujiajie/pa-chromium,bright-sparks/chromium-spacewalk,hgl888/chromium-crosswalk,ChromiumWebApps/chromium,ondra-novak/chromium.src,hujiajie/pa-chromium,Jonekee/chromium.src,anirudhSK/chromium,dushu1203/chromium.src,M4sse/chromium.src,dednal/chromium.src,markYoungH/chromium.src,jaruba/chromium.src,patrickm/chromium.src,Jonekee/chromium.src,fujunwei/chromium-crosswalk,nacl-webkit/chrome_deps,nacl-webkit/chrome_deps,patrickm/chromium.src,rogerwang/chromium,markYoungH/chromium.src,PeterWangIntel/chromium-crosswalk,ondra-novak/chromium.src,Pluto-tv/chromium-crosswalk,nacl-webkit/chrome_deps,Just-D/chromium-1,axinging/chromium-crosswalk,dushu1203/chromium.src,ltilve/chromium,mogoweb/chromium-crosswalk,zcbenz/cefode-chromium,krieger-od/nwjs_chromium.src,ondra-novak/chromium.src,nacl-webkit/chrome_deps,ltilve/chromium,nacl-webkit/chrome_deps,anirudhSK/chromium,Pluto-tv/chromium-crosswalk,ltilve/chromium,littlstar/chromium.src,hgl888/chromium-crosswalk,fujunwei/chromium-crosswalk,robclark/chromium,axinging/chromium-crosswalk,hgl888/chromium-crosswalk-efl,keishi/chromium,dushu1203/chromium.src,Pluto-tv/chromium-crosswalk,ChromiumWebApps/chromium,timopulkkinen/BubbleFish,krieger-od/nwjs_chromium.src,TheTypoMaster/chromium-crosswalk,robclark/chromium,hgl888/chromium-crosswalk,ChromiumWebApps/chromium,junmin-zhu/chromium-rivertrail,dushu1203/chromium.src,markYoungH/chromium.src,nacl-webkit/chrome_deps,dednal/chromium.src,crosswalk-project/chromium-crosswalk-efl,pozdnyakov/chromium-crosswalk,ondra-novak/chromium.src,nacl-webkit/chrome_deps,timopulkkinen/BubbleFish,TheTypoMaster/chromium-crosswalk,anirudhSK/chromium,junmin-zhu/chromium-rivertrail,patrickm/chromium.src,Jonekee/chromium.src,krieger-od/nwjs_chromium.src,littlstar/chromium.src,Just-D/chromium-1,hujiajie/pa-chromium,mogoweb/chromium-crosswalk,krieger-od/nwjs_chromium.src,ChromiumWebApps/chromium,chuan9/chromium-crosswalk,robclark/chromium,PeterWangIntel/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,zcbenz/cefode-chromium,anirudhSK/chromium,bright-sparks/chromium-spacewalk,PeterWangIntel/chromium-crosswalk,mogoweb/chromium-crosswalk,Chilledheart/chromium,rogerwang/chromium,dushu1203/chromium.src,mohamed--abdel-maksoud/chromium.src,Just-D/chromium-1,ChromiumWebApps/chromium,hgl888/chromium-crosswalk-efl,Pluto-tv/chromium-crosswalk,dednal/chromium.src,pozdnyakov/chromium-crosswalk,mogoweb/chromium-crosswalk,markYoungH/chromium.src,pozdnyakov/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,crosswalk-project/chromium-crosswalk-efl,rogerwang/chromium,ltilve/chromium,ChromiumWebApps/chromium,hujiajie/pa-chromium,Just-D/chromium-1,TheTypoMaster/chromium-crosswalk,Jonekee/chromium.src,keishi/chromium,Chilledheart/chromium,anirudhSK/chromium,littlstar/chromium.src,timopulkkinen/BubbleFish,Jonekee/chromium.src,M4sse/chromium.src,junmin-zhu/chromium-rivertrail,mohamed--abdel-maksoud/chromium.src,zcbenz/cefode-chromium,hgl888/chromium-crosswalk-efl,junmin-zhu/chromium-rivertrail,mohamed--abdel-maksoud/chromium.src,ondra-novak/chromium.src,patrickm/chromium.src,M4sse/chromium.src,jaruba/chromium.src,mogoweb/chromium-crosswalk,Chilledheart/chromium,ltilve/chromium,markYoungH/chromium.src,mogoweb/chromium-crosswalk,chuan9/chromium-crosswalk,hgl888/chromium-crosswalk,ChromiumWebApps/chromium,pozdnyakov/chromium-crosswalk,timopulkkinen/BubbleFish,pozdnyakov/chromium-crosswalk,pozdnyakov/chromium-crosswalk,Just-D/chromium-1,M4sse/chromium.src,krieger-od/nwjs_chromium.src,axinging/chromium-crosswalk,fujunwei/chromium-crosswalk,M4sse/chromium.src,ChromiumWebApps/chromium,littlstar/chromium.src,mogoweb/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,Jonekee/chromium.src,axinging/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,chuan9/chromium-crosswalk,fujunwei/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,rogerwang/chromium,jaruba/chromium.src,hgl888/chromium-crosswalk-efl,TheTypoMaster/chromium-crosswalk,hgl888/chromium-crosswalk-efl,keishi/chromium,crosswalk-project/chromium-crosswalk-efl,markYoungH/chromium.src,rogerwang/chromium,Fireblend/chromium-crosswalk,krieger-od/nwjs_chromium.src,krieger-od/nwjs_chromium.src,hgl888/chromium-crosswalk-efl,timopulkkinen/BubbleFish,chuan9/chromium-crosswalk,timopulkkinen/BubbleFish,markYoungH/chromium.src,dednal/chromium.src,axinging/chromium-crosswalk,zcbenz/cefode-chromium,zcbenz/cefode-chromium,hgl888/chromium-crosswalk-efl,rogerwang/chromium,robclark/chromium,markYoungH/chromium.src,zcbenz/cefode-chromium,zcbenz/cefode-chromium,keishi/chromium,dednal/chromium.src,TheTypoMaster/chromium-crosswalk,hujiajie/pa-chromium,nacl-webkit/chrome_deps,jaruba/chromium.src,hgl888/chromium-crosswalk-efl,PeterWangIntel/chromium-crosswalk,Fireblend/chromium-crosswalk,mogoweb/chromium-crosswalk,timopulkkinen/BubbleFish,ltilve/chromium,littlstar/chromium.src,ltilve/chromium,mohamed--abdel-maksoud/chromium.src,Fireblend/chromium-crosswalk,patrickm/chromium.src,M4sse/chromium.src,pozdnyakov/chromium-crosswalk,axinging/chromium-crosswalk,ChromiumWebApps/chromium,bright-sparks/chromium-spacewalk,TheTypoMaster/chromium-crosswalk,dednal/chromium.src,axinging/chromium-crosswalk,pozdnyakov/chromium-crosswalk,junmin-zhu/chromium-rivertrail,bright-sparks/chromium-spacewalk,keishi/chromium,littlstar/chromium.src,axinging/chromium-crosswalk,dushu1203/chromium.src,ltilve/chromium,Fireblend/chromium-crosswalk,crosswalk-project/chromium-crosswalk-efl,mohamed--abdel-maksoud/chromium.src,markYoungH/chromium.src,robclark/chromium,Just-D/chromium-1,keishi/chromium,ltilve/chromium