Only emit the personality function as a global value if the backend actually

supports it. This solves this error on the Darwin x86-64 platform:

$ cat testcase.ii
struct A {
  A();
};

A *bork() {
  return new A;
}
$ llvm-g++ -arch x86_64 -c testcase.ii
/var/tmp//cc3U8fd8.s:52:unknown section type: non_lazy_symbol_pointers
/var/tmp//cc3U8fd8.s:52:Rest of line ignored. 1st junk character valued 76 (L).
/var/tmp//cc3U8fd8.s:53:Unknown pseudo-op: .indirect_symbol
/var/tmp//cc3U8fd8.s:53:Rest of line ignored. 1st junk character valued 95 (_).

llvm-svn: 41999