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>

diff -durN gcc-4.5.2.orig/libjava/Makefile.in gcc-4.5.2/libjava/Makefile.in

--- gcc-4.5.2.orig/libjava/Makefile.in	2010-12-16 13:49:03.000000000 +0100

+++ gcc-4.5.2/libjava/Makefile.in	2010-12-29 23:02:41.000000000 +0100

@@ -9463,6 +9463,9 @@

 ecjx$(EXEEXT): $(ecjx_OBJECTS) $(ecjx_DEPENDENCIES) 

 	@rm -f ecjx$(EXEEXT)

 	$(ecjx_LINK) $(ecjx_OBJECTS) $(ecjx_LDADD) $(LIBS)

+ecjx.$(OBJEXT): $(ecjx_SOURCES)

+	@rm -f ecjx.$(OBJEXT)

+	$(CC_FOR_BUILD) $(BUILD_CFLAGS) -c -o $@ $<

 gappletviewer$(EXEEXT): $(gappletviewer_OBJECTS) $(gappletviewer_DEPENDENCIES) 

 	@rm -f gappletviewer$(EXEEXT)

 	$(gappletviewer_LINK) $(gappletviewer_OBJECTS) $(gappletviewer_LDADD) $(LIBS)