adding unit test for vx_malloc

tests/Makefile

@@ -1,4 +1,4 @@
-all: runtime regression opencl riscv
+all: runtime regression opencl riscv unittest
 
 runtime:
 	$(MAKE) -C runtime
@@ -12,10 +12,14 @@ opencl:
 riscv:
 	$(MAKE) -C riscv
 
+unittest:
+	$(MAKE) -C unittest
+
 clean:
 	$(MAKE) clean -C runtime
 	$(MAKE) clean -C regression
 	$(MAKE) clean -C opencl
 	$(MAKE) clean -C riscv
+	$(MAKE) clean -C unittest
 
-.PHONY: all runtime regression opencl riscv
+.PHONY: all runtime regression opencl riscv unittest