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

[Sergei Barannikov 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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s-barannikov wrote:

`IncludeStackMustBeEmpty` is only used in this if. Maybe just remove the parameter and the if/assert?

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