comptools: do not force build of make-3.81 unless really needed

On systems with make-3.82, we forcibly force the build and the use
of make-3.81

But some newer tools break when building with make-3.81. For example,
eglibc-3.18 breaks.

Introduce a new blind options that tools may select if they require
make-3.81. If the system does not have make-3.81, and this option is
selected, then we force the build of make-3.81. Otherwise, we leave
it to the user to decide on his own.

Note that no component selects this option for now. It will come in
later patches as we find them.

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

 # Compute MIPS-specific values

 CT_DoArchTupleValues() {

     local _64

     # The architecture part of the tuple

     if [ "${CT_ARCH_64}" = "y" ]; then

         _64="64"

     fi

     CT_TARGET_ARCH="${CT_ARCH}${_64}${CT_ARCH_SUFFIX:-${target_endian_el}}"

     # Override CFLAGS for endianness:

     case "${CT_ARCH_ENDIAN}" in

         big)    CT_ARCH_ENDIAN_CFLAG="-EB";;

         little) CT_ARCH_ENDIAN_CFLAG="-EL";;

     esac

     # Override ABI flags

     CT_ARCH_ABI_CFLAG="-mabi=${CT_ARCH_mips_ABI}"

     CT_ARCH_WITH_ABI="--with-abi=${CT_ARCH_mips_ABI}"

 }