The code instrumented with ASan may have its own instance of the

mach_override library.
In this case chances are that functions from it will be called from
mach_override_ptr() during ASan initialization.
This may lead to crashes (if those functions are instrumented) or
incorrect behavior (if the implementations differ).

The attached patch renames mach_override_ptr() into
__asan_mach_override_ptr() and makes the rest of the mach_override
internals hidden.
The corresponding AddressSanitizer bug is
http://code.google.com/p/address-sanitizer/issues/detail?id=22

Patch by glider@google.com

llvm-svn: 147303