[PATCH] MC: Improve the .fill directive's compatibility with GAS

[Rafael Ávila de Espíndola]

  LGTM, but please also add a test for "fill 1, 5, 1<<32".

  Jim Grosbach, is this OK with you (maybe with changing MCAsmStreamer::EmitIntValue in a followup patch)?

http://llvm-reviews.chandlerc.com/D2667