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>

 2008-04-28  Hiroki Kaminaga  <kaminaga@sm.sony.co.jp>

 	[BZ 6740]

 	nptl/sysdeps/powerpc/tcb-offsets.sym (PRIVATE_FUTEX_OFFSET):

 	Guard sym definition with #ifndef __ASSUME_PRIVATE_FUTEX.

 --- a/nptl/sysdeps/powerpc/tcb-offsets.sym

 +++ b/nptl/sysdeps/powerpc/tcb-offsets.sym

 @@ -15,4 +15,6 @@

  PID				thread_offsetof (pid)

  TID				thread_offsetof (tid)

  POINTER_GUARD			(offsetof (tcbhead_t, pointer_guard) - TLS_TCB_OFFSET - sizeof (tcbhead_t))

 +#ifndef __ASSUME_PRIVATE_FUTEX

  PRIVATE_FUTEX_OFFSET		thread_offsetof (header.private_futex)

 +#endif