[NFC][clang]Increase the number of driver diagnostics

We're close to hitting the limited number of driver diagnostics, increase `DIAG_SIZE_DRIVER` to accommodate more.

Reviewed By: erichkeane

Differential Revision: https://reviews.llvm.org/D114615
diff --git a/clang/include/clang/Basic/DiagnosticIDs.h b/clang/include/clang/Basic/DiagnosticIDs.h
index aef8651..375930c 100644
--- a/clang/include/clang/Basic/DiagnosticIDs.h
+++ b/clang/include/clang/Basic/DiagnosticIDs.h
@@ -30,7 +30,7 @@
     // Size of each of the diagnostic categories.
     enum {
       DIAG_SIZE_COMMON        =  300,
-      DIAG_SIZE_DRIVER        =  250,
+      DIAG_SIZE_DRIVER        =  300,
       DIAG_SIZE_FRONTEND      =  150,
       DIAG_SIZE_SERIALIZATION =  120,
       DIAG_SIZE_LEX           =  400,