[clang] [clang][Lex][NFC] Reorder SrcMgr checks in CheckMacroName (PR #141483)

[Shafik Yaghmour via cfe-commits]

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@@ -373,8 +373,8 @@ bool Preprocessor::CheckMacroName(Token &MacroNameTok, MacroUse isDefineUndef,
   // Macro names with reserved identifiers are accepted if built-in or passed
   // through the command line (the later may be present if -dD was used to
   // generate the preprocessed file).
-  if (!SourceMgr.isInPredefinedFile(MacroNameLoc) &&
-      !SourceMgr.isInSystemHeader(MacroNameLoc)) {
+  if (!SourceMgr.isInSystemHeader(MacroNameLoc) &&
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shafik wrote:

Seems like change deserves a note since it is not obvious the order matters or why.

https://github.com/llvm/llvm-project/pull/141483