[compiler-rt] Ensure AsanInitFromRtl is called from a static initializer on OS X...

[compiler-rt] Ensure AsanInitFromRtl is called from a static initializer on OS X by using ASAN_DYNAMIC=1

The idea is to ensure that the ASan runtime gets initialized early (i.e.
before other initializers/constructors) even when DYLD_INSERT_LIBRARIES
is not used. In that case, the interceptors are not installed (on OS X,
DYLD_INSERT_LIBRARIES is required for interceptors to work), and therefore
ASan gets currently initialized quite late -- from the main executable's
module initializer. The following issues are a consequence of this:

  https://code.google.com/p/address-sanitizer/issues/detail?id=363
  https://code.google.com/p/address-sanitizer/issues/detail?id=357

Both of them are fixed with this patch.

Reviewed at http://reviews.llvm.org/D7117

llvm-svn: 226929