Use digit separators in the diagnostic

Author: AaronBallman

clang/include/clang/Basic/DiagnosticLexKinds.td

@@ -91,7 +91,7 @@ def err_unterminated___pragma : Error<"missing terminating ')' character">;
 def err_conflict_marker : Error<"version control conflict marker in file">;
 
 def err_counter_overflow : Error<
-  "'__COUNTER__' value cannot exceed 2147483647">;
+  "'__COUNTER__' value cannot exceed 2'147'483'647">;
 def ext_counter : Extension<
   "'__COUNTER__' is a C2y extension">, InGroup<C2y>;
 def warn_counter : Warning<

clang/test/C/C2y/n3457_1.c

@@ -16,5 +16,5 @@ static_assert(__COUNTER__ == 2147483646); // Test and increment
 static_assert(__COUNTER__ == 2147483647); // Test and increment
 
 // This one should fail.
-signed long i = __COUNTER__; // expected-error {{'__COUNTER__' value cannot exceed 2147483647}}
+signed long i = __COUNTER__; // expected-error {{'__COUNTER__' value cannot exceed 2'147'483'647}}
 

clang/test/C/C2y/n3457_2.c

@@ -6,5 +6,5 @@
 // the value too large is fine. Expanding to a too-large value is not.
 #ifdef EXPAND_IT
   // This one should fail.
-  signed long i = __COUNTER__; // expected-error {{'__COUNTER__' value cannot exceed 2147483647}}
+  signed long i = __COUNTER__; // expected-error {{'__COUNTER__' value cannot exceed 2'147'483'647}}
 #endif