babeld: use TARGET_CONFIGURE_OPTS

As suggested by a previous submission of
babeld (https://patchwork.ozlabs.org/patch/631953/), we can use
TARGET_CONFIGURE_OPTS instead of passing CFLAGS and LDFLAGS in
PLATFORM_DEFINES.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/babeld/babeld.mk

@@ -10,8 +10,7 @@ BALELD_LICENSE = MIT
 BALELD_LICENSE_FILES = LICENSE
 
 define BABELD_BUILD_CMDS
-	$(MAKE) -C $(@D) CC="$(TARGET_CC)" \
-		PLATFORM_DEFINES="$(TARGET_CFLAGS) $(TARGET_LDFLAGS)"
+	$(MAKE) -C $(@D) $(TARGET_CONFIGURE_OPTS)
 endef
 
 define BABELD_INSTALL_TARGET_CMDS