Always check the function attribute to determine checksum mismatch for...

Always check the function attribute to determine checksum mismatch for available_externally functions (#87279)

This is to fix an assertion error. Apparently, `pseudo_probe_desc` could
still be available for import functions, and its checksum mismatch state
can be different from import function's `profile-checksum-mismatch`
attr. This happens when unstable IR or ODR violation issue occurs, the
definitions of the same function across different translation units
could be different and result in different checksums. During link time
deduplication, the internal function definition (the checksum in desc is
computed based on) is substituted by the `available_externally`
definition, which cause the inconsistency. Hence, we fix it to by always
checking the state for the new `available_externally` definition, which
is saved in the function attribute.