[msan] Better handling of signed compare

[eugenis]

#110880 triggers a false positive in MSan.

Improve handleSignedRelationalComparison to handle the kind of IR generated with that change; or enable exact handling (-msan-handle-icmp-exact) at the cost of ~3% code size and (unknown) CPU.

[goldsteinn]

Do you still want me to revert a646436? Happy to do so.

[vitalybuka]

Do you still want me to revert a646436? Happy to do so.

Yes please! It will take some time to optimize -msan-handle-icmp-exact.

Please mention this issue in revert, so we can reland when msan is fixed.

[goldsteinn]

Do you still want me to revert a646436? Happy to do so.

Yes please! It will take some time to optimize -msan-handle-icmp-exact.

Please mention this issue in revert, so we can reland when msan is fixed.

see you did so, thank you. Can you ping back on the PR when recommit is okay?

[vitalybuka]

@goldsteinn Let see if this one is not reverted and try to reland #110880 tomorrow.