[llvm] [TableGen] Use assert instead of PrintFatalError in TGLexer. NFC. (PR #122303)

[Jay Foad via llvm-commits]

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@@ -664,11 +663,10 @@ bool TGLexer::prepExitInclude(bool IncludeStackMustBeEmpty) {
   PrepIncludeStack.pop_back();
 
   if (IncludeStackMustBeEmpty) {
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jayfoad wrote:

Yeah, I wasn't sure how far to go with cleanups like that in this patch.

https://github.com/llvm/llvm-project/pull/122303