[release/9.0-staging] JIT: avoid fp divide by zero in profile synthesis #113418
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This can trip up users that have enabled floating point exceptions. While we don't generally support changing the exception modes we also can easily avoid dividing by zero here. Addresses #113369
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Backport of #113396 to release/9.0-staging
/cc @AndyAyersMS
Customer Impact
Unexpected floating-point divide by zero exception. While we generally don't support running managed code with FP exceptions enabled, we also should not be generating such exceptions needlessly.
There is precedent for us back porting this kind of change, see eg: #76334
Regression
.NET 9 added a fair amount of FP processing to the JIT that wasn't there in .NET 8.
Testing
Verified the JIT will no longer cause FP exception from this computation.
Risk
Low, no diffs in SPMI.