ARMAsmBackend: Use fixupNeedsRelaxationAdvanced. NFC
This prepares for the upcoming change to simplify relocation recording
in MCAssembler.
While both MCAssembler::fixupNeedsRelaxation and
MCAssembler::handleFixup call evaluateFixup and use
shouldForceRelocation, the shouldForceRelocation logic is not supposed
to be needed by MCAssembler::fixupNeedsRelaxation.
The ARM special cases for interworking branches
(https://reviews.llvm.org/D33436 and https://reviews.llvm.org/D33898)
break the assumption. Switch to fixupNeedsRelaxationAdvanced and
explicitly test the conditions.
