linux: allow builds to override libdir path
linux: allow builds to override libdir path

Not all multilibs install into /usr/lib/, so when building for one which
doesn't, we hit errors where the detected python arch does not match the
detected target arch.  Like x86_64/powerpc64/sparc64/etc... which use
/usr/lib64/.

Review URL: http://codereview.chromium.org/8018002

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@103422 0039d316-1c4b-4281-b951-d872f2087c98

yitian134/chromium,adobe/chromium,adobe/chromium,gavinp/chromium,yitian134/chromium,ropik/chromium,adobe/chromium,yitian134/chromium,gavinp/chromium,adobe/chromium,yitian134/chromium,adobe/chromium,gavinp/chromium,gavinp/chromium,yitian134/chromium,ropik/chromium,ropik/chromium,adobe/chromium,adobe/chromium,ropik/chromium,yitian134/chromium,gavinp/chromium,ropik/chromium,adobe/chromium,adobe/chromium,yitian134/chromium,gavinp/chromium,gavinp/chromium,ropik/chromium,gavinp/chromium,yitian134/chromium,yitian134/chromium,yitian134/chromium,adobe/chromium,gavinp/chromium,gavinp/chromium,ropik/chromium,adobe/chromium,ropik/chromium,ropik/chromium