Move function into cpp file under KMP_AFFINITY_SUPPORTED guard.

When affinity isn't supported, __kmp_affinity_compact doesn't exist.  The
problem is that in kmp_affinity.h there is a function which uses it without the
proper KMP_AFFINITY_SUPPORTED guard around it.  The compiler was smart enough to
ignore it and the function __kmp_affinity_cmp_Address_child_num which relies on
it, but I think it is cleaner to have it under the proper guard.  Since the
function is only used in the kmp_affinity.cpp file and there aren't any plans to
have it elsewhere.  I have moved it there.

llvm-svn: 280542