[ASan] Make init-order checker allow access to already initialized globals.

This change adds ASan runtime option "strict-init-order" (off by default)
that makes init-order checker bark if global initializer accesses any global from different
translation unit (even if the latter is already initialized). strict init-order checking
doesn't play well with, e.g. LLVM registration machineries, and causes issue 
https://code.google.com/p/address-sanitizer/issues/detail?id=178.

llvm-svn: 179843