gen_package_auxiliary drops the condition of a dependency such as
+BUILD_NLS:libintl-full, so the ABI version check of a package also
counts packages that it does not depend on in this configuration.
With all packages selected and BUILD_NLS not set, libelf depends on
libintl-full. gettext-full is built after elfutils, and its new
libintl-full.version causes elfutils, and binutils, gdb, strace,
iproute2 and others through it, to be built again on the next make
call.
Write the condition as a make expression with get_conditional_dep, as
gen_package_mk does.
Signed-off-by: John Crispin <john@phrozen.org>