build: add default host build recipes for gnulib

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 <[email protected]>
Link: openwrt/openwrt#15853
Signed-off-by: Robert Marko <[email protected]>

include/host-build.mk

@@ -44,6 +44,15 @@ define Host/Prepare
   $(call Host/Prepare/Default)
 endef
 
+define Host/Gnulib/Prepare
+  $(STAGING_DIR_HOST)/bin/gnulib-tool \
+	--local-dir=$(STAGING_DIR_HOST)/share/gnulib \
+	--source-base=$(PKG_GNULIB_BASE) \
+	$(PKG_GNULIB_ARGS) \
+	$(PKG_GNULIB_MODS) \
+  ;
+endef
+
 HOST_CONFIGURE_VARS = \
 	CC="$(HOSTCC)" \
 	CFLAGS="$(HOST_CFLAGS)" \
@@ -107,6 +116,10 @@ define Host/Compile
   $(call Host/Compile/Default)
 endef
 
+define Host/Gnulib/Compile
+  $(call Host/Compile/Default,SUBDIRS='$$$$(wildcard $(PKG_GNULIB_BASE))')
+endef
+
 define Host/Install/Default
 	$(call Host/Compile/Default,install)
 endef