Fixes#185277
ForceFunctionAttrs currently only checks the `alwaysinline`/`noinline`
conflict when forcing function attributes. This is incomplete, because
LLVM verifier rules define additional incompatible function attribute
combinations.
Extend hasConflictingFnAttr() to reject more conflicting function
attributes, including combinations involving `optnone`, `minsize`,
`optsize`, and `optdebug`.
Also add required companion attributes when forcing function attributes:
`optnone` requires `noinline`, so forceattrs now adds `noinline`
automatically when needed.
769ffa0133