[tablegen] A couple of changes to ClangDiagnosticEmmitter.
[tablegen] A couple of changes to ClangDiagnosticEmmitter.

-Emit an empty warning option as string ("") instead of 0.
-For diagnostic names also emit the size of the string.


git-svn-id: a4a6f32337ebd29ad4763b423022f00f68d1c7b7@132046 91177308-0d34-0410-b5e6-96231b3b80d8

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