Revert "ARC: build: retire old toggles"

Revert "ARC: build: retire old toggles"

This has caused a bunch of build failures at a few sites, with GNU
2015.12 and older as the assembler seems to need -mlock to be able to
grok llock/scond instructions for ARC700 builds.
different places since the
older tools still seem to release
of tools which most people are using seem to trip with the -mlock flag
not being passed.

This reverts commit c3005475889c7c730638f95d13be3360f0b33e98.