Make libuwind target thread safe

Author: jonringer

sdk/cpprt/Makefile

@@ -75,7 +75,8 @@ all: $(CPPRT)
 prepare-libunwind:
 	$(CP) linux/pthread_compat.h $(LIBUNWIND_DIR)/include
 
-$(CPPRT): $(OBJS) prepare-libunwind libunwind
+$(CPPRT): $(OBJS) prepare-libunwind
+        $(Make) libunwind
 	$(CP) $(LIBUNWIND_DIR)/src/.libs/libunwind.a $(CPPRT)
 	$(AR) rs $@ $(OBJS)