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

[ro]

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.

[ro]

ping

I know it's not yet been a week, but I'm away until new year. Maybe someone has a chance to look at it?

Thanks.

[ro]

Could someone please commit this for me?

[ro]

It would be really nice if someone could commit this for me.

Thanks.

Rainer

[ro]

Anyone to commit this for me?

Thanks.

Rainer

compiler-rt/trunk/lib/sanitizer_common/sanitizer_internal_defs.h

 # define SANITIZER_INTERFACE_WEAK_DEF(ReturnType, Name, ...)                   \
   extern "C" SANITIZER_INTERFACE_ATTRIBUTE SANITIZER_WEAK_ATTRIBUTE            \
   ReturnType Name(__VA_ARGS__)
 #endif
 
 // SANITIZER_SUPPORTS_WEAK_HOOKS means that we support real weak functions that
 // will evaluate to a null pointer when not defined.
 #ifndef SANITIZER_SUPPORTS_WEAK_HOOKS
-#if (SANITIZER_LINUX || SANITIZER_MAC || SANITIZER_SOLARIS) && !SANITIZER_GO
+#if (SANITIZER_LINUX || SANITIZER_SOLARIS) && !SANITIZER_GO
+# define SANITIZER_SUPPORTS_WEAK_HOOKS 1
+// Before Xcode 4.5, the Darwin linker doesn't reliably support undefined
+// weak symbols.  Mac OS X 10.9/Darwin 13 is the first release only supported
+// by Xcode >= 4.5.
+#elif SANITIZER_MAC && \
+    __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >= 1090 && !SANITIZER_GO
 # define SANITIZER_SUPPORTS_WEAK_HOOKS 1
 #else
 # define SANITIZER_SUPPORTS_WEAK_HOOKS 0
 #endif
 #endif // SANITIZER_SUPPORTS_WEAK_HOOKS
 // For some weak hooks that will be called very often and we want to avoid the
 // overhead of executing the default implementation when it is not necessary,
 // we can use the flag SANITIZER_SUPPORTS_WEAK_HOOKS to only define the default