portmap: fix static linking

Portmap builds and links, however, does not get built correctly when
BR2_PREFER_STATIC_LIB is selected.  There are no dynamic libraries in
rootfs.tar, however, portmap gets linked dynamically without regards to
the PREFER_STATIC_LIB tags.  LDFLAGS was not being passed into the build of
portmap.

Signed-off-by:  Andy Kennedy <andy.kennedy@adtran.com>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/portmap/portmap.mk

@@ -17,8 +17,7 @@ PORTMAP_FLAGS += NO_FORK=1
 endif
 
 define PORTMAP_BUILD_CMDS
-	CFLAGS="$(TARGET_CFLAGS)" \
-	$(MAKE) CC="$(TARGET_CC)" -C $(@D) $(PORTMAP_FLAGS)
+	$(TARGET_CONFIGURE_OPTS) $(MAKE) -C $(@D) $(PORTMAP_FLAGS)
 endef
 
 define PORTMAP_INSTALL_TARGET_CMDS