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_64=y

CT_ARCH_powerpc=y

CT_KERNEL_linux=y

CT_KERNEL_V_2_6_31=y

CT_BINUTILS_V_2_20_1a=y

CT_BINUTILS_FOR_TARGET=y

CT_CC_V_4_5_2=y

CT_CC_LANG_FORTRAN=y

CT_CC_LANG_CXX=y

CT_CC_LANG_JAVA=y

CT_LIBC_glibc=y

CT_LIBC_GLIBC_V_2_9=y

# CT_LIBC_GLIBC_FORCE_UNWIND is not set

CT_DEBUG_gdb=y

CT_GDB_NATIVE=y

CT_GMP_V_5_0_1=y

CT_MPFR_V_3_0_0=y

CT_CLOOG_V_0_15_10=y

CT_MPC_V_0_8_2=y