[clang][PP] Add extension to predefine target OS macros (#74676)

Add an extension feature `define-target-os-macros` that enables clang to
provide definitions of common TARGET_OS_* conditional macros. The
extension is enabled in the Darwin toolchain driver.

1 files changed, 7 insertions, 0 deletions

diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 56de0f7..b33bdad 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -4365,6 +4365,9 @@ static void GeneratePreprocessorArgs(const PreprocessorOptions &Opts,
   if (Opts.SourceDateEpoch)
     GenerateArg(Consumer, OPT_source_date_epoch, Twine(*Opts.SourceDateEpoch));
 
+  if (Opts.DefineTargetOSMacros)
+    GenerateArg(Consumer, OPT_fdefine_target_os_macros);
+
   // Don't handle LexEditorPlaceholders. It is implied by the action that is
   // generated elsewhere.
 }
@@ -4463,6 +4466,10 @@ static bool ParsePreprocessorArgs(PreprocessorOptions &Opts, ArgList &Args,
   if (isStrictlyPreprocessorAction(Action))
     Opts.LexEditorPlaceholders = false;
 
+  Opts.DefineTargetOSMacros =
+      Args.hasFlag(OPT_fdefine_target_os_macros,
+                   OPT_fno_define_target_os_macros, Opts.DefineTargetOSMacros);
+
   return Diags.getNumErrors() == NumErrorsBefore;
 }