configure: add possibility to set arbitrary variable in check_for

If check_for is able to find the required prog/inc/lib, allow it to
set an arbitrary variable to 'y'. This variable is then pushed down
to the kconfig definition.

For example:
has_or_abort prog=foobar kconfig=has_foobar

If foobar is available, it yields a kconfig variable defaulting to y:
config CONFIGURE_has_foobar
bool
default y

If foobar is missing, it yields a kconfig variable defaulting to n:
config CONFIGURE_has_foobar
bool

Thus it is possible to depends on that variabel to show/hide options:
config SOME_FEATURE
bool
prompt "Some feature"
depends on CONFIGURE_has_foobar

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

 --- binutils/bfd/elf64-ppc.c.jj	2004-09-27 16:46:06.000000000 -0400

 +++ binutils/bfd/elf64-ppc.c	2004-10-04 09:09:50.000000000 -0400

 @@ -9681,7 +9681,12 @@ ppc64_elf_relocate_section (bfd *output_

  	      else if (!SYMBOL_REFERENCES_LOCAL (info, &h->elf)

  		       && !is_opd

  		       && r_type != R_PPC64_TOC)

 -		outrel.r_info = ELF64_R_INFO (h->elf.dynindx, r_type);

 +		{

 +		  outrel.r_info = ELF64_R_INFO (h->elf.dynindx, r_type);

 +		  if (h->elf.dynindx == -1

 +		      && h->elf.root.type == bfd_link_hash_undefweak)

 +		  memset (&outrel, 0, sizeof outrel);

 +		}

  	      else

  		{

  		  /* This symbol is local, or marked to become local,