ninja: make cross-compilation use $CC/$CXX for the target compiler 
ninja: make cross-compilation use $CC/$CXX for the target compiler 

Took over from http://codereview.chromium.org/9649016/ 

BUG=None 
TEST=set CC/CXX to cross-compiler, set GYP_CROSSCOMPILE to 1, run gyp, ninja chrome. 



git-svn-id: e7e1075985beda50ea81ac4472467b4f6e91fc78@1448 78cadc50-ecff-11dd-a971-7dbc132099af

tarc/gyp,bnq4ever/gypgoogle,enkripsi/gyp,okwasi/gyp,svn2github/kgyp,svn2github/gyp,sdklite/gyp,MIPS/external-chromium_org-tools-gyp,sanyaade-teachings/gyp,brson/gyp,duanhjlt/gyp,clar/gyp,bpsinc-native/src_tools_gyp,mapbox/gyp,sdklite/gyp,ttyangf/gyp,enkripsi/gyp,saghul/gyn,Danath/gyp,ttyangf/pdfium_gyp,erikge/watch_gyp,brson/gyp,mapbox/gyp,lukeweber/gyp-override,sloanyang/gyp,Chilledheart/gyp,omasanori/gyp,pandaxcl/gyp,pyokagan/gyp,AWhetter/gyp,yjhjstz/gyp,geekboxzone/lollipop_external_chromium_org_tools_gyp,enkripsi/gyp,kevinchen3315/gyp-git,svn2github/kgyp,duanhjlt/gyp,svn2github/gyp,mistydemeo/gyp,openpeer/webrtc-gyp,LazyCodingCat/gyp,sanyaade-teachings/gyp,ryfx/gyp,tarc/gyp,omasanori/gyp,MIPS/external-chromium_org-tools-gyp,kevinchen3315/gyp-git,sdklite/gyp,erikge/watch_gyp,IllusionRom-deprecated/android_platform_external_chromium_org_tools_gyp,pyokagan/gyp,lukeweber/gyp-override,bnq4ever/gypgoogle,bulldy80/gyp_unofficial,bdarnell/gyp,xin3liang/platform_external_chromium_org_tools_gyp,Danath/gyp,yinquan529/platform-external-chromium_org-tools-gyp,Jack-Q/GYP-copy,sloanyang/gyp,IllusionRom-deprecated/android_platform_external_chromium_org_tools_gyp,Jack-Q/GYP-copy,mapbox/gyp,MIPS/external-chromium_org-tools-gyp,AWhetter/gyp,LazyCodingCat/gyp,sanyaade-teachings/gyp,chromium/gyp,amoikevin/gyp,cysp/gyp,ryfx/gyp,turbulenz/gyp,tarc/gyp,yjhjstz/gyp,chromium/gyp,sport-monkey/GYP,openpeer/webrtc-gyp,pandaxcl/gyp,channing/gyp,AOSPU/external_chromium_org_tools_gyp,azunite/gyp,xin3liang/platform_external_chromium_org_tools_gyp,mistydemeo/gyp,bpsinc-native/src_tools_gyp,lianliuwei/gyp,sanyaade-teachings/gyp,azunite/gyp_20150930,LazyCodingCat/gyp,mapbox/gyp,Phuehvk/gyp,adblockplus/gyp,svn2github/gyp,svn2github/kgyp,amoikevin/gyp,clar/gyp,mgamer/gyp,bnq4ever/gypgoogle,tarc/gyp,azunite/gyp,xin3liang/platform_external_chromium_org_tools_gyp,sanyaade-teachings/gyp,bulldy80/gyp_unofficial,enkripsi/gyp,LazyCodingCat/gyp,IllusionRom-deprecated/android_platform_external_chromium_org_tools_gyp,erikge/watch_gyp,okumura/gyp,duanhjlt/gyp,yangrongwei/gyp,omasanori/gyp,yangrongwei/gyp,channing/gyp,Chilledheart/gyp,dougbeal/gyp,enkripsi/gyp,pyokagan/gyp,springmeyer/gyp,AOSPU/external_chromium_org_tools_gyp,clar/gyp,Chilledheart/gyp,cysp/gyp,luvit/gyp,trafi/gyp,svn2github/kgyp,azunite/gyp,sloanyang/gyp,kevinchen3315/gyp-git,Danath/gyp,mgamer/gyp,cchamberlain/gyp,ttyangf/gyp,Phuehvk/gyp,dougbeal/gyp,sdklite/gyp,android-ia/platform_external_chromium_org_tools_gyp,geekboxzone/lollipop_external_chromium_org_tools_gyp,turbulenz/gyp,pandaxcl/gyp,sdklite/gyp,mumble-voip/libmumble-gyp,bnoordhuis/gyp,svn2github/gyp,luvit/gyp,Omegaphora/external_chromium_org_tools_gyp,channing/gyp,dougbeal/gyp,adblockplus/gyp,azunite/gyp,azunite/gyp_20150930,okwasi/gyp,carlTLR/gyp,Danath/gyp,duanhjlt/gyp,yjhjstz/gyp,bpsinc-native/src_tools_gyp,tarc/gyp,yjhjstz/gyp,brson/gyp,dougbeal/gyp,ryfx/gyp,luvit/gyp,alexcrichton/gyp,carlTLR/gyp,clar/gyp,okumura/gyp,xin3liang/platform_external_chromium_org_tools_gyp,bulldy80/gyp_unofficial,azunite/gyp,cchamberlain/gyp,bnq4ever/gypgoogle,saghul/gyn,lianliuwei/gyp,mistydemeo/gyp,ttyangf/gyp,svn2github/kgyp,yinquan529/platform-external-chromium_org-tools-gyp,Chilledheart/gyp,adblockplus/gyp,cchamberlain/gyp,yjhjstz/gyp,mumble-voip/libmumble-gyp,carlTLR/gyp,trafi/gyp,Phuehvk/gyp,okumura/gyp,ttyangf/pdfium_gyp,openpeer/webrtc-gyp,ryfx/gyp,Jack-Q/GYP-copy,amoikevin/gyp,saghul/gyn,cysp/gyp,bnoordhuis/gyp,Danath/gyp,springmeyer/gyp,pandaxcl/gyp,ttyangf/pdfium_gyp,mumble-voip/libmumble-gyp,lianliuwei/gyp,AWhetter/gyp,lianliuwei/gyp,svn2github/gyp,duanhjlt/gyp,Chilledheart/gyp,turbulenz/gyp,adblockplus/gyp,lukeweber/gyp-override,sport-monkey/GYP,turbulenz/gyp,alexcrichton/gyp,msc-/gyp,sport-monkey/GYP,bnoordhuis/gyp,mkrautz/gyp-libmumble,bulldy80/gyp_unofficial,trafi/gyp,springmeyer/gyp,okumura/gyp,mistydemeo/gyp,cysp/gyp,clar/gyp,Phuehvk/gyp,azunite/gyp_20150930,amoikevin/gyp,msc-/gyp,IllusionRom-deprecated/android_platform_external_chromium_org_tools_gyp,bnq4ever/gypgoogle,mgamer/gyp,erikge/watch_gyp,Phuehvk/gyp,okwasi/gyp,chromium/gyp,bpsinc-native/src_tools_gyp,luvit/gyp,erikge/watch_gyp,alexcrichton/gyp,Jack-Q/GYP-copy,azunite/gyp_20150930,mgamer/gyp,ttyangf/pdfium_gyp,android-ia/platform_external_chromium_org_tools_gyp,LazyCodingCat/gyp,omasanori/gyp,cysp/gyp,bdarnell/gyp,ttyangf/gyp,geekboxzone/lollipop_external_chromium_org_tools_gyp,yinquan529/platform-external-chromium_org-tools-gyp,AOSPU/external_chromium_org_tools_gyp,yangrongwei/gyp,dougbeal/gyp,AWhetter/gyp,mapbox/gyp,pandaxcl/gyp,android-ia/platform_external_chromium_org_tools_gyp,pyokagan/gyp,pyokagan/gyp,msc-/gyp,openpeer/webrtc-gyp,carlTLR/gyp,yangrongwei/gyp,AWhetter/gyp,mkrautz/gyp-libmumble,bulldy80/gyp_unofficial,msc-/gyp,amoikevin/gyp,saghul/gyn,mkrautz/gyp-libmumble,azunite/gyp_20150930,chromium/gyp,sport-monkey/GYP,brson/gyp,alexcrichton/gyp,okwasi/gyp,bnoordhuis/gyp,springmeyer/gyp,trafi/gyp,mkrautz/gyp-libmumble,bnoordhuis/gyp,kevinchen3315/gyp-git,cchamberlain/gyp,MIPS/external-chromium_org-tools-gyp,carlTLR/gyp,AOSPU/external_chromium_org_tools_gyp,sport-monkey/GYP,channing/gyp,mgamer/gyp,springmeyer/gyp,turbulenz/gyp,ttyangf/gyp,Omegaphora/external_chromium_org_tools_gyp,trafi/gyp,Omegaphora/external_chromium_org_tools_gyp,lukeweber/gyp-override,Jack-Q/GYP-copy,geekboxzone/lollipop_external_chromium_org_tools_gyp,cchamberlain/gyp,bdarnell/gyp,Omegaphora/external_chromium_org_tools_gyp,chromium/gyp,adblockplus/gyp,ttyangf/pdfium_gyp,sloanyang/gyp,bdarnell/gyp,android-ia/platform_external_chromium_org_tools_gyp,msc-/gyp,openpeer/webrtc-gyp,ryfx/gyp,saghul/gyn,mumble-voip/libmumble-gyp,yinquan529/platform-external-chromium_org-tools-gyp