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>