Convert codebase to C89 compatibility and update test scripts

v0/include.mk

@@ -11,6 +11,8 @@ V0_TEST_OBJ := $(patsubst v0/%.c,v0/bin/%.o,$(V0_TEST))
 V0_SRC_DEPS := $(V0_SRC_OBJ:.o=.d)
 V0_TEST_DEPS := $(V0_TEST_OBJ:.o=.d)
 
+CFLAGS += -Werror -Wall -pedantic -std=c89
+
 v0/bin/c2: $(V0_SRC_OBJ)
 	$(CC) $(CFLAGS) -o $@ $^
 
@@ -19,8 +21,16 @@ V0_SRC_OBJ_NO_MAIN := $(filter-out v0/bin/main.o,$(V0_SRC_OBJ))
 v0/bin/test: $(V0_SRC_OBJ_NO_MAIN) $(V0_TEST_OBJ)
 	$(CC) $(CFLAGS) -o $@ $^
 
+# Only run tests under valgrind on Linux. On macOS (Darwin) valgrind is
+# typically unavailable or unsupported, so run the test binary directly.
+ifeq ($(shell uname -s),Linux)
+TEST_CMD := valgrind --quiet --leak-check=full --error-exitcode=1 v0/bin/test
+else
+TEST_CMD := v0/bin/test
+endif
+
 test:: v0/bin/test
-	valgrind --quiet --leak-check=full --error-exitcode=1 v0/bin/test
+	$(TEST_CMD)
 
 generate_golden:: v0/bin/test
 	GENERATE_GOLDEN=1 v0/bin/test