[clang] Clean up denormal handling with -ffp-model, -ffast-math, etc. (PR #89477)

[Matt Arsenault via cfe-commits]

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@@ -1462,6 +1460,14 @@ floating point semantic models: precise (the default), strict, and fast.
   "allow_approximate_fns", "off", "off", "on"
   "allow_reassociation", "off", "off", "on"
 
+The ``-fp-model`` option does not modify the "fdenormal-fp-math" or
+"fdenormal-fp-math-f32" settings, but it does have an impact on whether
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arsenm wrote:

IIRC denormal-fp-math-f32 is only a cc1 flag not exposed to end users 

https://github.com/llvm/llvm-project/pull/89477