[Sanitizer] Use __libc_malloc/__libc_free instead of malloc/free inside internal allocator on Linux (important for TSan)

llvm-svn: 158261

llvm-svn: 158144

[Sanitizer] Allocator for internal runtime purposes. Currently it calls libcmalloc, but we might have to make it more low-level in future

llvm-svn: 158142