The PathScale compiler silently accepts unknown options that start in
more than one '-':

  $ touch foo.c
  $ pathcc -c foo.c --junk
  $ echo $?
  0
  $ pathcc -c foo.c ---junk
  $ echo $?
  0
  $ pathcc -c foo.c -junk
  pathcc ERROR parsing -junk: unknown flag
  $ echo $?
  2

We teach the TryCompile to pass a bogus flag with only one '-' instead
of three '-'s for this compiler.