Bump DiagnosticSemaKinds count; we're close to hitting it.

 $ grep '= DIAG_START_SEMA' include/clang/Basic/DiagnosticIDs.h
       DIAG_START_ANALYSIS      = DIAG_START_SEMA            + 3000
 $ grep 'def ' include/clang/Basic/DiagnosticSemaKinds.td | wc -l
       2994

llvm-svn: 259728