Add generic recipes for incorporating gnulib into a build
for simplification and readability of the individual build Makefile.
Recipes for configuring and installing are purposefully missing
since "configuring" gnulib is done with standard autoreconf
and gnulib is not a final build target meant for installing.
Signed-off-by: Michael Pratt <mcpratt@pm.me>
Link: https://github.com/openwrt/openwrt/pull/15853
Signed-off-by: Robert Marko <robimarko@gmail.com>
