package/pkgconf: make the pkg-config wrapper relocatable

This change refactors the pkg-config wrapper template and the way it is filled
in a way there is no longer hard-coded paths to the staging directory; so it
is now fully relocatable.

package/pkgconf/pkg-config.in

@@ -1,2 +1,4 @@
 #!/bin/sh
-PKG_CONFIG_LIBDIR=${PKG_CONFIG_LIBDIR:-@PKG_CONFIG_LIBDIR@} PKG_CONFIG_SYSROOT_DIR=${PKG_CONFIG_SYSROOT_DIR:-@STAGING_DIR@} $(dirname $0)/pkgconf @STATIC@ $@
+STAGING_DIR="$(readlink -f "$(dirname "$0")/../..")/@STAGING_SUBDIR@"
+TARGET_PKG_CONFIG_LIBDIR="$( echo @PKG_CONFIG_LIBDIR@ | sed -e "s@^@${STAGING_DIR}/@ ; s@:@:${STAGING_DIR}/@g" )"
+PKG_CONFIG_LIBDIR=${PKG_CONFIG_LIBDIR:-${TARGET_PKG_CONFIG_LIBDIR}} PKG_CONFIG_SYSROOT_DIR=${PKG_CONFIG_SYSROOT_DIR:-${STAGING_DIR}} $(dirname $0)/pkgconf @STATIC@ $@

package/pkgconf/pkgconf.mk

@@ -19,8 +19,12 @@ endef
 define HOST_PKGCONF_INSTALL_WRAPPER
 	$(INSTALL) -m 0755 -D package/pkgconf/pkg-config.in \
 		$(HOST_DIR)/usr/bin/pkg-config
-	$(SED) 's,@PKG_CONFIG_LIBDIR@,$(STAGING_DIR)/usr/lib/pkgconfig:$(STAGING_DIR)/usr/share/pkgconfig,' \
-		-e 's,@STAGING_DIR@,$(STAGING_DIR),' \
+	# @PKG_CONFIG_LIBDIR@ is a colon-separated list of paths to search.
+	# These paths are relative to the root of the staging directory; they will
+	# be automatically prefixed with the staging directory path by the wrapper
+	# at runtime to ensure its relocatability.
+	$(SED) 's,@PKG_CONFIG_LIBDIR@,/usr/lib/pkgconfig:/usr/share/pkgconfig,' \
+		-e 's,@STAGING_SUBDIR@,$(STAGING_SUBDIR),' \
 		$(HOST_DIR)/usr/bin/pkg-config
 endef