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>

 CT_EXPERIMENTAL=y

 CT_LOCAL_TARBALLS_DIR="${HOME}/src"

 CT_SAVE_TARBALLS=y

 CT_LOG_EXTRA=y

 CT_ARCH_mips=y

 CT_TARGET_VENDOR="malta"

 CT_KERNEL_linux=y

 CT_KERNEL_V_2_6_38=y

 CT_BINUTILS_V_2_21_1a=y

 CT_CC_V_4_4_6=y

 # CT_CC_GCC_USE_GRAPHITE is not set

 CT_LIBC_EGLIBC_V_2_13=y

 CT_DEBUG_gdb=y

 # CT_GDB_GDBSERVER_STATIC is not set

 CT_GDB_V_7_2a=y

 CT_GMP_V_5_0_1=y

 CT_MPFR_V_3_0_0=y

 CT_TEST_SUITE_GCC=y