Add tests exercising substitution of arguments in function-like macros.

This capability is the only thing that makes function-like macros
interesting. This isn't supported yet so these tests fail for now.

tests/016-define-func-1-arg.c

@@ -0,0 +1,2 @@
+#define foo(x) ((x) + 1)
+foo(bar)

tests/017-define-func-2-args.c

@@ -0,0 +1,2 @@
+#define foo(x,y) ((x)*(y))
+foo(bar,baz)