pkgconfig: make Requires for libconfig optional

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>

configure.ac

@@ -36,12 +36,18 @@ AS_IF([test "x$with_libconfig" = xyes], [
 			    AC_DEFINE(HAVE_LIBCONFIG_15, 1, [detected libconfig equal to or greater than 1.5]),
 			    AC_DEFINE(HAVE_LIBCONFIG_15, 0, []))
 			  ])
+	libconfig_req="libconfig"
 	CFLAGS="$CFLAGS $LIBCONFIG_CFLAGS"
 	LIBS="$LIBS $LIBCONFIG_LIBS"
 ], [
+	libconfig_req=""
 	enable_gadget_schemes=no
 ])
 
+REQUIRES="$libconfig_req"
+
+AC_SUBST([REQUIRES])
+
 AM_CONDITIONAL(BUILD_EXAMPLES, [test "x$enable_examples" = xyes])
 
 AS_IF([test "x$enable_tests" = xyes], [

libusbgx.pc.in

@@ -5,7 +5,7 @@ includedir=@includedir@
 
 Name: libusbgx
 Description: USB gadget-configfs library
-Requires: libconfig
+Requires: @REQUIRES@
 Version: @PACKAGE_VERSION@
 Libs: -L${libdir} -lusbgx
 Cflags: -I${includedir}