[clang] Add clang atomic control options and attribute (PR #114841)

[Erich Keane via cfe-commits]

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@@ -5958,6 +5968,58 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
 
   RenderFloatingPointOptions(TC, D, OFastEnabled, Args, CmdArgs, JA);
 
+  if (Arg *AtomicArg = Args.getLastArg(options::OPT_fatomic_EQ)) {
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erichkeane wrote:

IMO, we need a separate function for this, given how complicated this is.  WHICH also makes me wonder; why are we letting this be this complicated.  DO we do something similar/that would be sufficient for other flags?  This whole thing below is really getting complicated.

ALSO, we need to make sure these round-trip, so make sure that they go th rough the 'Render' stuff correctly.

https://github.com/llvm/llvm-project/pull/114841