Find libmsgpackc in Multi-Arch library paths

The msgpack library may be present in /usr/lib or /usr/lib/$arch,
but only the former is being searched.  Check both places and fix the
library name to use the C lib (libmsgpackc) rather than the C++ lib
(libmsgpack).

Signed-off-by: James McCoy <jamessan@jamessan.com>

Makefile

@@ -14,11 +14,11 @@ ifneq ($(findstring yes,$(shell pkg-config --exists msgpack && echo yes)),)
 	CFLAGS += -DMSGPACK=1 $(shell pkg-config --cflags msgpack)
 	LDFLAGS += $(shell pkg-config --libs msgpack)
 else
-	MSGPACK_LIB=$(shell ls /usr/lib/libmsgpack.so 2>/dev/null)
+	MSGPACK_LIB=$(shell ls /usr/lib/libmsgpackc.so /usr/lib/*/libmsgpackc.so 2>/dev/null)
 	ifneq ($(strip $(MSGPACK_LIB)),)
 		FORMAT_OBJS += formats/msgpack.o
 		CFLAGS += -DMSGPACK=1
-		LDFLAGS += -lmsgpack
+		LDFLAGS += -lmsgpackc
 	endif
 endif