Some time ago, the sanitizers as of r315899 were imported into gcc mainline. This broke
bootstrap on Darwin 10 and 11, as reported in GCC PR sanitizer/82824
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82824) due to the unconditional use
of VM_MEMORY_OS_ALLOC_ONCE. This was only introduced in Darwin 13/Mac OS X 10.9.
The use of the macro was introduced in r300450.
I couldn't find any statement which Darwin versions are supposed to be supported by
LLVM, but the trivial patch to use the macro only if present allowed the gcc bootstrap
So far, I haven't tried building llvm/compiler-rt on Darwin 11. Maybe the patch is
simple enough to go in nonetheless.