TableGen: AsmMatcher support for better operand diagnostics.
TableGen: AsmMatcher support for better operand diagnostics.

"Invalid operand" may be a completely correct diagnostic, but it's often
insufficiently specific to really help identify and fix the problem in
assembly source. Allow a target to specify a more-specific diagnostic kind
for each AsmOperandClass derived definition and use that to provide
more detailed diagnostics when an operant of that class resulted in a
match failure.

rdar://8987109

git-svn-id: a4a6f32337ebd29ad4763b423022f00f68d1c7b7@159050 91177308-0d34-0410-b5e6-96231b3b80d8

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