[clang] [Preprocessor] Do not expand macros if the input is already preprocessed (PR #137665)

[Juan Manuel Martinez Caamaño via cfe-commits]

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@@ -1558,6 +1558,13 @@ void clang::InitializePreprocessor(Preprocessor &PP,
                                    const PCHContainerReader &PCHContainerRdr,
                                    const FrontendOptions &FEOpts,
                                    const CodeGenOptions &CodeGenOpts) {
+
+  if (all_of(FEOpts.Inputs,
+             [](const FrontendInputFile &FI) { return FI.isPreprocessed(); })) {
+    PP.SetDisableMacroExpansion();
+    return;
+  }
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jmmartinez wrote:

You're right, it makes more sense there. I've updated it to match.

https://github.com/llvm/llvm-project/pull/137665