[NFC] Adding a note about the macro __FLT_EVAL_METHOD__

[zahiraam]

Summary

This is to clarify that the macro FLT_EVAL_METHOD it is not pre-defined like other preprocessor macros. It will not appear when preprocessor macros are dumped.

[aaron.ballman]

clang/docs/UsersManual.rst

1610–1618

I reworked this a bit more -- does it still seem correct to you?

[zahiraam]

clang/docs/UsersManual.rst

1610–1618

Yes. Thanks (long sentences :).

[aaron.ballman]

LGTM, thanks for the cleanup here!

clang/docs/UsersManual.rst

.. option:: -f[no-]protect-parens:
    modes, such as `-ffp-model=precise` or `-ffp-model=strict`, this option
    has no effect because the optimizer is prohibited from making unsafe
    transformations.
 
 .. _FLT_EVAL_METHOD:
 
 A note about ``__FLT_EVAL_METHOD__``
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 The macro ``__FLT_EVAL_METHOD__`` will expand to either the value set from the
 command line option ``ffp-eval-method`` or to the value from the target info
-setting. The ``__FLT_EVAL_METHOD__`` macro cannot expand to the correct
-evaluation method in the presence of a ``#pragma`` which alters the evaluation
-method. An error is issued if ``__FLT_EVAL_METHOD__`` is expanded inside a scope
-modified by ``#pragma clang fp eval_method``.
+setting. The ``__FLT_EVAL_METHOD__`` macro is resolved as a macro
+definition during expansion. When predefined preprocessor macros are dumped,
+``__FLT_EVAL_METHOD__`` will not be listed.
+The ``__FLT_EVAL_METHOD__`` macro cannot expand to the correct evaluation method
+in the presence of a ``#pragma`` which alters the evaluation method. An error is
+issued if ``__FLT_EVAL_METHOD__`` is expanded inside a scope modified by
+``#pragma clang fp eval_method``.
 
 .. _fp-constant-eval:
 
 A note about Floating Point Constant Evaluation
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 In C, the only place floating point operations are guaranteed to be evaluated
 during translation is in the initializers of variables of static storage