comptools: add make-3.81

Since the advent of make-3.82, some packages now break due to changes
in make-3.82, being stricter than 3.81 when interpreting the Makefiles.

This has bugged us a bit too much so far, and I believe fixing all
of them is a long road, while simply building make-3.81 is the easiest
route for now.

Of course, in the long term, packages will get fixed upstream, and we
should back-port the fixes to old versions, and get rid of building
make-3.81. In the meantime...

Reported several times on the mailing list.

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

# Options specific to crosstool-NG acting as a backend

config IS_A_BACKEND

    string

    option env="CT_IS_A_BACKEND"

config BACKEND

    bool

    default y if IS_A_BACKEND =  "y" || IS_A_BACKEND =  "Y"

    default n if IS_A_BACKEND != "y" && IS_A_BACKEND != "Y"

config BACKEND_ARCH

    string

    option env="CT_BACKEND_ARCH"

config BACKEND_KERNEL

    string

    option env="CT_BACKEND_KERNEL"

config BACKEND_LIBC

    string

    option env="CT_BACKEND_LIBC"