Mark the at_exit and at_quick_exit tests as unsupported under C++98 an 03,...

Mark the at_exit and at_quick_exit tests as unsupported under C++98 an 03, since those calls were introduced in C++11.  They're already guarded by an ifdef in the code, so this is a 'belt-and-suspenders' change.

llvm-svn: 339804