GCN: Remove 'last_arg' spec function
The LLVM 13.0.1 assembler ('llvm-mc') indeed still does complain in presence of
multiple '-mcpu=[...]' options:
as: for the --mcpu option: may only occur zero or one times!
However, as of
"GCN: Tag '-march=[...]', '-mtune=[...]' as 'Negative' of themselves [PR112669]",
the GCC-side special handling is no longer necessary.
gcc/
* config.gcc <amdgcn-*-amdhsa> (extra_gcc_objs): Don't set.
* config/gcn/driver-gcn.cc: Remove.
* config/gcn/gcn-hsa.h (ASM_SPEC, EXTRA_SPEC_FUNCTIONS): Remove
'last_arg' spec function.
* config/gcn/t-gcn-hsa (driver-gcn.o): Remove.