Currently the opt + debug combo just results in build_mode=dbg getting set. We want to support flagging off of when the user has BOTH opt and dbg set, so in this case opt_debug should be used.

AKA:

Currently its

SCons opt=on, dbg=off -> bazel --//bazel/config:build_mode=opt_on
SCons opt=off, dbg=on -> bazel --//bazel/config:build_mode=dbg
SCons opt=on, dbg=on -> bazel --//bazel/config:build_mode=dbg

It should be

SCons opt=on, dbg=off -> bazel --//bazel/config:build_mode=opt_on
SCons opt=off, dbg=on -> bazel --//bazel/config:build_mode=dbg
SCons opt=on, dbg=on -> bazel --//bazel/config:build_mode=opt_debug