[Sanitizers, Darwin] Disable SANITIZER_SUPPORTS_WEAK_HOOKS before Mac OS X 10.9

[Sanitizers, Darwin] Disable SANITIZER_SUPPORTS_WEAK_HOOKS before Mac OS X 10.9

Summary:
Before Xcode 4.5, undefined weak symbols don't work reliably on Darwin:
https://stackoverflow.com/questions/6009321/weak-symbol-link-on-mac-os-x
Therefore this patch disables their use before Mac OS X 10.9 which is the first version
only supported by Xcode 4.5 and above.

Reviewers: glider, kcc, vitalybuka

Reviewed By: vitalybuka

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D41346

llvm-svn: 324284