Patch from Filipe Cabecinhas that uses argparse in dotest.py instead of a hand...

Patch from Filipe Cabecinhas that uses argparse in dotest.py instead of a hand coded option. I made a few modifications:

Changed the '-A' option to also have a long option of '--arch'. This is now specified multiple times to get multiple architectures.

Old: -A i386^x86_64
New: -A i386 -A x86_64
     --arch i386 --arch x86_64
     
Changed the '-C' option to also have a long option of '--compiler'. This is now specified multiple times to get multiple compiler.

Old: -C clang^gcc
New: -C clang -C gcc
     --compiler clang --compiler gcc
llvm-svn: 163141