A series of Clang-related powerpc commits

r310146:
  Use the right bitwise OR operation for clearing single-step at trap time.
r311912:
  Force all TOC references in asm to include '@toc'
r312369:
  Use the explicit expanded form of cmp.
r312617:
  Hide the 'MOREARGS' macro, it conflicts with contrib code, and is only used
  in one file.
r312614:
  Don't pass -Wa,-many through clang, the integrated as doesn't support it.
r312659:
  Avoid using non-zero argument for __builtin_frame_address().
r312974:
  Add a INTR_TRIG_INVALID, and use it in the powerpc interrupt code.
r312977:
  Force the setting of bit 7 in the sysmouse packet byte 1 to be unsigned.
r313005:
  Update CFLAGS for clang compatibility
r314826:
  Clang in base now supports -mlongcall, so remove this hack