rtmpdump: use TARGET_LDFLAGS instead of TARGET_CFLAGS for XLDFLAGS

The XLDFLAGS is for ld related flags so use TARGET_LDFLAGS instead of
TARGET_CFLAGS, also the TARGET_CFLAGS is already used for XCFLAGS.

This fix is also needed for supporting the per-package staging directory.

Signed-off-by: Fabio Porcedda <fabio.porcedda@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/rtmpdump/rtmpdump.mk

@@ -39,7 +39,7 @@ define RTMPDUMP_BUILD_CMDS
 	$(MAKE) CRYPTO=$(RTMPDUMP_CRYPTO) \
 		prefix=/usr \
 		XCFLAGS="$(RTMPDUMP_CFLAGS)" \
-		XLDFLAGS="$(TARGET_CFLAGS)" \
+		XLDFLAGS="$(TARGET_LDFLAGS)" \
 		CROSS_COMPILE="$(TARGET_CROSS)" \
 		$(RTMPDUMP_SHARED) \
 		-C $(@D)/librtmp