ldc2/sdc2 now emit slightly worse diagnostics for MIPS-I. The problem
is that they don't trigger the custom parser because all the candidates
are disabled by feature bits. On all other subtargets, the diagnostics are
accurate but are subject to the usual issues of needing to report multiple
ways to correct the code (e.g. smaller offset, enable a CPU feature) but
only being able to report one error.
Depends on D18435