[SPARC] Don't emit deprecated FP branches when targeting v9

Don't emit deprecated v8-style FP compares & branches when targeting v9
processors.

For now, always use %fcc0, because currently the allocator requires allocatable
registers to also be spillable, which isn't the case with v9 FCC registers.

The work to enable allocation over the entire FCC register file will be done in
a future patch.

Fixes bug #17834

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D135515