add codegen and args tests, fix couple of bugs in C generation

tests/args.scm

@@ -0,0 +1,55 @@
+;;; Splitting the command line at `--'.
+;;;
+;;; getopt-long cannot do this: it consumes the separator and merges
+;;; everything after it into `@' alongside the input file. So sexc
+;;; splits the raw argv first, and only the head is parsed as options.
+;;; Everything else reaches the C compiler exactly as written --
+;;; including the words that do not start with a dash, which a previous
+;;; leading-dash heuristic used to drop.
+
+(import sexc)
+
+(define full '("foo.sex" "-o" "bar" "--" "-framework" "OpenGL" "-Wall"))
+
+(test-group "argument separator"
+
+  (test "options and input file stay with sexc"
+        '("foo.sex" "-o" "bar")
+        (args-before-separator full))
+
+  (test "the tail reaches the compiler verbatim"
+        '("-framework" "OpenGL" "-Wall")
+        (args-after-separator full))
+
+  ;; The case that motivated this: `OpenGL' has no leading dash and was
+  ;; silently dropped, leaving `-framework' to swallow whatever flag
+  ;; came next.
+  (test "a word without a dash survives"
+        '("-framework" "OpenGL")
+        (args-after-separator '("x.sex" "--" "-framework" "OpenGL")))
+
+  (test "no separator means nothing for the compiler"
+        '()
+        (args-after-separator '("foo.sex" "-o" "bar")))
+
+  (test "no separator leaves every argument with sexc"
+        '("foo.sex" "-o" "bar")
+        (args-before-separator '("foo.sex" "-o" "bar")))
+
+  (test "a trailing separator is allowed"
+        '()
+        (args-after-separator '("foo.sex" "--")))
+
+  (test "a leading separator leaves no input file"
+        '()
+        (args-before-separator '("--" "-lm")))
+
+  ;; Only the first `--' separates; a later one is an ordinary compiler
+  ;; argument (ld takes several).
+  (test "only the first separator counts"
+        '("-Wl,--as-needed" "--" "-lm")
+        (args-after-separator '("x.sex" "--" "-Wl,--as-needed" "--" "-lm")))
+
+  (test "an empty command line is handled"
+        '()
+        (args-before-separator '())))