This patch is to support ongoing work for replacing "GCC/BFD" by "CLANG/LLD" on target PowerPC64 , by proposing a way to specify and/or locate a secondary ld.bfd linker.
This is necessary as LLD currently doesn't support PowerPC 32 bits, so we keep using BFD for the 32 bit stuff on PowePC64(LIB32 compatibility and STAND/slof/loader.)
- creates LD_BFD variable pointing to ld.bfd
- use LD_BFD as linker for LIB32/compat
- Default behavior for other platforms aren't changed.