[llvm] [TableGen] Use SmallVectors for preprocessor include stack. NFC. (PR #121571)

[Jay Foad via llvm-commits]

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@@ -1055,20 +1048,16 @@ bool TGLexer::prepSkipDirectiveEnd() {
 }
 
 bool TGLexer::prepIsProcessingEnabled() {
-  for (const PreprocessorControlDesc &I :
-       llvm::reverse(*PrepIncludeStack.back()))
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jayfoad wrote:

I did think about that, but really if you have nested #ifs I don't see any reason why the inner (or outer) condition would have a higher chance of being false.

https://github.com/llvm/llvm-project/pull/121571