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

isInPredefinedFile() will look at the presumed loc, which is
comparatively slow. Move it after isInSystemFile().


http://llvm-compile-time-tracker.com/compare.php?from=843e362318e884991e517a54446b4faeacdad789&to=de0421a1a38052042721a67a6094f5cb38431f26&stat=instructions:u

Author: tbaederr

clang/lib/Lex/PPDirectives.cpp

@@ -373,8 +373,10 @@ 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)) {
+  // NB: isInPredefinedFile() is relatively expensive, so keep it at the end
+  // of the condition.
+  if (!SourceMgr.isInSystemHeader(MacroNameLoc) &&
+      !SourceMgr.isInPredefinedFile(MacroNameLoc)) {
     MacroDiag D = MD_NoWarn;
     if (isDefineUndef == MU_Define) {
       D = shouldWarnOnMacroDef(*this, II);