Fix C89 warnings about variables at top of scope, enums, variadic macros

Add extern UnityFixture in internals header. Add C89 target in Makefile
 clang will show these warnings but can suppress "//" with -Wno-comment.

extras/fixture/test/Makefile

@@ -34,6 +34,11 @@ noStdlibMalloc: ../build/
 	@ echo "build with noStdlibMalloc"
 	./$(TARGET)
 
+clang89: ../build/
+	clang $(CFLAGS) $(DEFINES) $(SRC) $(INC_DIR) -o $(TARGET) -m32 -std=c89 -Wno-comment
+	clang $(CFLAGS) $(DEFINES) $(SRC) $(INC_DIR) -o $(TARGET) -m32 \
+		-D UNITY_EXCLUDE_STDLIB_MALLOC -std=c89 -Wno-comment ; ./$(TARGET)
+
 clangEverything:
 	clang $(CFLAGS) $(DEFINES) $(SRC) $(INC_DIR) -o $(TARGET) -m64 -Weverything
 
@@ -56,5 +61,6 @@ CFLAGS += -Wstrict-overflow=5
 CFLAGS += -Wstrict-prototypes
 CFLAGS += -Wswitch-default
 CFLAGS += -Wundef
+CFLAGS += -Wno-error=undef  # Warning only, this should not stop the build
 CFLAGS += -Wunused
 CFLAGS += -fstrict-aliasing