libpng: fix paths in config files

Signed-off-by: Rosen Penev <rosenp@gmail.com>

libs/libpng/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=libpng
 PKG_VERSION:=1.6.37
-PKG_RELEASE:=7
+PKG_RELEASE:=8
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.xz
 PKG_SOURCE_URL:=@SF/libpng
@@ -48,9 +48,9 @@ TARGET_LDFLAGS += -lz
 
 define Build/InstallDev
 	$(call Build/InstallDev/cmake,$(1))
-	$(SED) \
-		's,^\(prefix\|exec_prefix\)=.*,\1=$(STAGING_DIR)/usr,g' \
-		$(1)/usr/bin/libpng{,16}-config
+	$(SED) 's,^\(prefix\|exec_prefix\)=.*,\1=$(STAGING_DIR)/usr,g' $(1)/usr/bin/libpng{,16}-config
+	$(SED) '/^includedir=/s|/usr|$$$${prefix}|' $(1)/usr/bin/libpng{,16}-config
+	$(SED) '/^libdir=/s|/usr|$$$${prefix}|' $(1)/usr/bin/libpng{,16}-config
 	$(SED) 's,/usr/include,$$$${prefix}/include,g' $(1)/usr/lib/pkgconfig/libpng16.pc
 	$(SED) 's,/usr/lib,$$$${exec_prefix}/lib,g' $(1)/usr/lib/pkgconfig/libpng16.pc
 	$(INSTALL_DIR) $(2)/bin