[clang] Bump up DIAG_SIZE_SEMA by 500 for downstream diagnostics.

Recently added HLSL diagnostics (89fb849) pushed the Swift compiler over
the existing limit.

rdar://135126738

Author: lhames

clang/include/clang/Basic/DiagnosticIDs.h

@@ -39,7 +39,7 @@ namespace clang {
       DIAG_SIZE_AST           =  300,
       DIAG_SIZE_COMMENT       =  100,
       DIAG_SIZE_CROSSTU       =  100,
-      DIAG_SIZE_SEMA          = 4500,
+      DIAG_SIZE_SEMA          = 5000,
       DIAG_SIZE_ANALYSIS      =  100,
       DIAG_SIZE_REFACTORING   = 1000,
       DIAG_SIZE_INSTALLAPI    =  100,