Updated build-llvm-byfl to work under OS X
Updated build-llvm-byfl to work under OS X

OS X's mktemp command lacks support for double-dash option variants
(e.g., --directory and --tmpdir) and has no equivalent of --suffix.
This revision attempts to work around those shortcomings.

losalamos/Byfl,losalamos/Byfl,losalamos/Byfl,losalamos/Byfl