configure: define FOO_CFLAGS/FOO_LIBS so that they are never empty

This allows us to simply pass the already exported variables to invoked
configures, where the non-empty values will override the detection logic
there.

Change-Id: I7353a313814c58922e34843aeae380e5afa442ca

libcdr/ExternalProject_libcdr.mk

@@ -57,18 +57,12 @@ else
 $(call gb_ExternalProject_get_state_target,libcdr,build) :
 	cd $(EXTERNAL_WORKDIR) \
 	&& PKG_CONFIG="" \
-	WPD_CFLAGS=" $(WPD_CFLAGS)" \
-	WPD_LIBS=" $(WPD_LIBS)" \
-	WPG_CFLAGS=" $(WPG_CFLAGS)" \
-	WPG_LIBS=" $(WPG_LIBS)" \
 	$(if $(filter YES,$(SYSTEM_LCMS2)),\
 	LCMS2_CFLAGS=" $(LCMS2_CFLAGS)" \
 	LCMS2_LIBS=" $(LCMS2_LIBS)", \
 	LCMS2_CFLAGS="-I$(call gb_UnpackedTarball_get_dir,lcms2/include) \
 	$(if $(filter MACOSX,$(OS)),-Wno-long-long)" \
 	LCMS2_LIBS="-L$(OUTDIR)/lib -llcms2" ) \
-	ZLIB_CFLAGS=" $(ZLIB_CFLAGS)" \
-	ZLIB_LIBS=" $(ZLIB_LIBS)" \
 	./configure \
 		--with-pic \
 		--enable-static \

libvisio/ExternalProject_libvisio.mk

@@ -56,14 +56,6 @@ else
 $(call gb_ExternalProject_get_state_target,libvisio,build) :
 	cd $(EXTERNAL_WORKDIR) \
 	&& PKG_CONFIG="" \
-	WPD_CFLAGS=" $(WPD_CFLAGS)" \
-	WPD_LIBS=" $(WPD_LIBS)" \
-	WPG_CFLAGS=" $(WPG_CFLAGS)" \
-	WPG_LIBS=" $(WPG_LIBS)" \
-	LIBXML_CFLAGS=" $(LIBXML_CFLAGS)" \
-	LIBXML_LIBS=" $(LIBXML_LIBS)" \
-	ZLIB_CFLAGS=" $(ZLIB_CFLAGS)" \
-	ZLIB_LIBS=" $(ZLIB_LIBS)" \
 	./configure \
 		--with-pic \
 		--enable-static \

mythes/ExternalProject_mythes.mk

@@ -21,8 +21,6 @@ $(call gb_ExternalProject_get_state_target,mythes,build):
 	cd $(EXTERNAL_WORKDIR) \
 	&& LIBS="$(gb_STDLIBS) $(LIBS)" ./configure --disable-shared --with-pic \
 	$(if $(filter YES,$(CROSS_COMPILING)),--build=$(BUILD_PLATFORM) --host=$(HOST_PLATFORM) gio_can_sniff=no) \
-	HUNSPELL_CFLAGS=" $(HUNSPELL_CFLAGS)" \
-	HUNSPELL_LIBS=" $(HUNSPELL_LIBS)" \
 	$(if $(filter C52U,$(COM)$(CPU)),CFLAGS="-m64") \
 	&& $(MAKE) \
 	&& touch $@