pkgconf: use relative path to STAGING_DIR instead of absolute path

The pkg-config wrapper script is currently generated with absolute
paths to $(STAGING_DIR). However, this will not work properly with
per-package SDK, and each package will be built with a different
STAGING_DIR value.

In order to fix this, we adjust how the pkg-config wrapper script is
generated, so that it uses a relative path to itself: the sysroot (i.e
STAGING_DIR) is always located in $(path of
pkg-config)/../$(STAGING_SUBDIR).

This change is independent from the per-package SDK work, and could be
applied independently from it.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/pkgconf/pkg-config.in

@@ -1,2 +1,5 @@
 #!/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@ $@
+PKGCONFDIR=$(dirname $0)
+DEFAULT_PKG_CONFIG_LIBDIR=${PKGCONFDIR}/../@STAGING_SUBDIR@/usr/lib/pkgconfig:${PKGCONFDIR}/../@STAGING_SUBDIR@/usr/share/pkgconfig
+DEFAULT_PKG_CONFIG_SYSROOT_DIR=${PKGCONFDIR}/../@STAGING_SUBDIR@
+PKG_CONFIG_LIBDIR=${PKG_CONFIG_LIBDIR:-${DEFAULT_PKG_CONFIG_LIBDIR}} PKG_CONFIG_SYSROOT_DIR=${PKG_CONFIG_SYSROOT_DIR:-${DEFAULT_PKG_CONFIG_SYSROOT_DIR}} ${PKGCONFDIR}/pkgconf @STATIC@ $@

package/pkgconf/pkgconf.mk

@@ -19,8 +19,7 @@ endef
 define HOST_PKGCONF_INSTALL_WRAPPER
 	$(INSTALL) -m 0755 -D package/pkgconf/pkg-config.in \
 		$(HOST_DIR)/bin/pkg-config
-	$(SED) 's,@PKG_CONFIG_LIBDIR@,$(STAGING_DIR)/usr/lib/pkgconfig:$(STAGING_DIR)/usr/share/pkgconfig,' \
-		-e 's,@STAGING_DIR@,$(STAGING_DIR),' \
+	$(SED) 's,@STAGING_SUBDIR@,$(STAGING_SUBDIR),g' \
 		$(HOST_DIR)/bin/pkg-config
 endef