Makefile generator: fix relative paths to submakefiles
Makefile generator: fix relative paths to submakefiles

gyp can be ran from a directory other than the source root.
The relative paths we put into the root Makefile must be relative to
the source root.

Review URL: http://codereview.chromium.org/159661

git-svn-id: e7e1075985beda50ea81ac4472467b4f6e91fc78@563 78cadc50-ecff-11dd-a971-7dbc132099af

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