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>

 diff -dur uClibc-0.9.28.1.orig/libc/sysdeps/linux/common/Makefile uClibc-0.9.28.1/libc/sysdeps/linux/common/Makefile

 --- uClibc-0.9.28.1.orig/libc/sysdeps/linux/common/Makefile	2007-01-26 00:54:19.000000000 +0100

 +++ uClibc-0.9.28.1/libc/sysdeps/linux/common/Makefile	2007-02-01 08:44:37.000000000 +0100

 @@ -25,6 +25,10 @@

  SRCS := $(filter-out sbrk.c,$(SRCS))

  endif

 +ifneq ($(strip $(UCLIBC_HAS_LFS)),y)

 +SRCS := $(filter-out readahead.c,$(SRCS))

 +endif

 +

  ifneq ($(strip $(UCLIBC_HAS_SSP)),y)

  SRCS := $(filter-out ssp.c,$(SRCS))

  endif