Add 'isCodeGenOnly' bit to Instruction .td records.  - Used to mark fake instructions which don't correspond to an actual machine    instruction (or are duplicates of a real instruction). This is to be used for    "special cases" in the .td files, which should be ignored by things like the    assembler and disassembler. We still need a good solution to handle pervasive    duplication, like with the Int_ instructions.
Add 'isCodeGenOnly' bit to Instruction .td records.
 - Used to mark fake instructions which don't correspond to an actual machine
   instruction (or are duplicates of a real instruction). This is to be used for
   "special cases" in the .td files, which should be ignored by things like the
   assembler and disassembler. We still need a good solution to handle pervasive
   duplication, like with the Int_ instructions.

 - Set the bit on fake "mov 0" style instructions, which allows turning an
   assembler matcher warning into a hard error.

 - -2 FIXMEs.


git-svn-id: a4a6f32337ebd29ad4763b423022f00f68d1c7b7@78731 91177308-0d34-0410-b5e6-96231b3b80d8

lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx