[PATCH] Make thumb the default instruction set for v7m and v7em

[Bernard Ogden]

  An alternative approach would be to enable thumb by default on all targets that support thumb2 - which would be more compatible with modern (hard-float) gccs.

  But that's likely a bit more controversial than simply fixing the 7M targets, so I'll prepare a separate patch.

http://llvm-reviews.chandlerc.com/D2062