_controlfp_s: Describe effects of FPCR changes on ARM

[olologin]

We believe this note should be somewhere close to _controlfp_s documentation.
More details:
https://stackoverflow.com/questions/78917793/windows-on-arm-math-is-not-trapping

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[Court72]

@TylerMSFT

Can you review the proposed changes?

Important: When the changes are ready for publication, adding a #sign-off comment is the best way to signal that the PR is ready for the review team to merge.

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[TylerMSFT]

Hi, we are looking into this.

[olologin]

Of course it is better to make it possible to enable exception handling, at least optionally. Because it doesn't look like a good idea to disable them for all ARM CPUs without a way to enable them, just because some ARM CPUs don't support it.

But that is not documentation-related.