Integrate unit tests into TAP build system

Adds unit_tests target to test/tap/Makefile so that unit tests are
built alongside existing TAP tests via 'make build_tap_tests'. Also
adds the unit test directory to clean/cleanall targets.

test/tap/Makefile

@@ -3,10 +3,10 @@
 
 .DEFAULT: all
 .PHONY: all
-all: tests tests_with_deps
+all: tests tests_with_deps unit_tests
 
 .PHONY: debug
-debug: tests tests_with_deps
+debug: tests tests_with_deps unit_tests
 
 .PHONY: test_deps
 test_deps:
@@ -29,6 +29,11 @@ tests_with_deps: tap test_deps
 	cd tests_with_deps && CC=${CC} CXX=${CXX} ${MAKE} $(MAKECMDGOALS)
 
 
+.PHONY: unit_tests
+unit_tests: tap
+	cd tests/unit && CC=${CC} CXX=${CXX} ${MAKE} $(MAKECMDGOALS)
+
+
 .PHONY: clean_utils
 .SILENT: clean_utils
 clean_utils:
@@ -40,6 +45,7 @@ clean:
 	cd tap && ${MAKE} -s clean
 	cd tests && ${MAKE} -s clean
 	cd tests_with_deps && ${MAKE} -s clean
+	cd tests/unit && ${MAKE} -s clean
 
 .PHONY: cleanall
 .SILENT: cleanall
@@ -48,3 +54,4 @@ cleanall:
 	cd tap && ${MAKE} -s cleanall
 	cd tests && ${MAKE} -s clean
 	cd tests_with_deps && ${MAKE} -s clean
+	cd tests/unit && ${MAKE} -s clean