[clang] [C2y] Support WG14 N3457, the __COUNTER__ macro (PR #162662)

[Aaron Ballman via cfe-commits]

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@@ -226,7 +226,7 @@ class Preprocessor {
       LangOptions::FPEvalMethodKind::FEM_UnsetOnCommandLine;
 
   // Next __COUNTER__ value, starts at 0.
-  unsigned CounterValue = 0;
+  unsigned long CounterValue = 0;
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AaronBallman wrote:

I went with `unsigned long` because the standard requires the value to fit within a `signed long` explicitly; so it was for parity with the standards wording. WDYT?

https://github.com/llvm/llvm-project/pull/162662