Don't run dsymutil when making a fat executable direct source.

 - Otherwise, we will end up with stray .dSYM files which don't get
   lipo'ed or removed.

 - Ideally we would run dsymutil on the result, but we don't have the
   infrastructure for that yet. Note that gcc doesn't handle this case
   either.

 - <rdar://problem/6809621> [driver] clang leaves .dSYM files lying
   around in tmp.

llvm-svn: 69951