The cmake check for whether libatomic could be used had been
unconditionally setting the result to false. Which was somewhat
fortunate, because the prerequisite check for whether it was *needed*
was always claiming it was, even if it was not.
However, this made platforms where libatomic is actually necessary
fail to link.
Differential Revision: http://reviews.llvm.org/D10453
llvm-svn: 239819
It is possible for the atomic routines to be provided by the compiler without
requiring any additional libraries. Check if that is the case before checking
for a library.
Patch by Matt Glazar!
llvm-svn: 230452
