MIPS16 cannot handle constant pools created by CTTZ table lookup
expansion. This causes "Cannot select" errors when trying to select
MipsISD::Lo nodes for constant pool addresses.
Modify the table lookup conditions to check ConstantPool operation
status, and only set ConstantPool to Custom in non-MIPS16 mode in MIPS
backend.
This ensures MIPS16 uses the ISD::CTPOP instead of attempting
unsupported constant pool operations.
Fix#61055.
1e42c76d61