Fix up diagnostics.

Move some diagnostics around between Diagnostic*Kinds.td files.  Diagnostics
used in multiple places were moved to DiagnosticCommonKinds.td.  Diagnostics
listed in the wrong place (ie, Sema diagnostics listed in
DiagnosticsParseKinds.td) were moved to the correct places.  One diagnostic
split into two so that the diagnostic string is in the .td file instead of in
code.  Cleaned up the diagnostic includes after all the changes.

llvm-svn: 349125