binutils/binutils: add blind option to force use of ld.bfd during build

gold is not capable of building glibc/eglibc, so we have to
force using the BFD linker, ld.bfd.

Offer a blind option that affected components can select to
force use of the BFD linker during the build.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

# Compute Blackfin-specific values

CT_DoArchTupleValues() {

    # The architecture part of the tuple:

    CT_TARGET_ARCH="bfin"

    # gcc ./configure flags

    CT_ARCH_WITH_ARCH=

    CT_ARCH_WITH_ABI=

    CT_ARCH_WITH_CPU=

    CT_ARCH_WITH_TUNE=

    CT_ARCH_WITH_FPU=

    CT_ARCH_WITH_FLOAT=

}