Fix tests C compile

I don't understand why I can't get strdup defined in Dictionary.cake.

src/Dictionary.cake

@@ -566,7 +566,7 @@
 
 (comptime-cond
  ('auto-test
-  (c-import "stdio.h")
+  (c-import "<stdio.h>" "<string.h>")
   (defun test--dictionary (&return int)
     (scope ;; Simple key value entries
      (defstruct dictionary-entry
@@ -613,6 +613,8 @@
      (var my-dictionary (addr complex-dictionary-entry) null)
      (strdict-use-key-arena my-dictionary)
 
+     (declare-extern-function strdup (str (addr (const char)) &return (addr char)))
+
      (var items (array complex-dictionary-entry)
        (array
         (array (strdup "cakelisp") "programming language" "cakelisp is a programming language")

src/Introspection.cake

@@ -1,5 +1,8 @@
 (import "FileUtilities.cake"
         "CHelpers.cake" "ComptimeHelpers.cake")
+(comptime-cond
+ ('Unix
+  (c-preprocessor-define __USE_XOPEN_EXTENDED))) ;; for strdup
 (c-import "<stdlib.h>" ;; atoi, atof
           "<string.h>" ;; strcmp
           "<ctype.h>" ;; For isspace
@@ -1829,9 +1832,12 @@
     (ignore))
 
   (defun test--introspection (&return int)
+    ;; (declare-extern-function strdup (str (addr (const char)) &return (addr char)))
+    (var another-name (addr char) (strdup "Another name"))
+    (defer (free another-name))
     (var a my-struct
       (array #"#"Hello!" This is a naughty
- naughty string with \\ backslashes and such \\#"# "Other name" (strdup "Another name") null
+ naughty string with \\ backslashes and such \\#"# "Other name" another-name null
              42 -0.33f (array 0.f 1.f 2.f) (array 10.f 20.f 30.f)
              (array (array "Hi" true) (array "Bye" false))
              false 'a'
@@ -1906,7 +1912,7 @@
 
     (scope ;; Copy structs
      (var a-2 my-struct
-       (array "Test struct" "Other name" (strdup "Another name") null
+       (array "Test struct" "Other name" another-name null
               42 -0.33f (array 0.f 1.f 2.f) (array 10.f 20.f 30.f)
               (array (array "Hi" true) (array "Bye" false))
               false 'a'
@@ -1925,8 +1931,7 @@
        (fprintf stderr "error: copied struct does not equal baseline\n")
        (return 1))
      (free-introspect-struct-fields
-      my-struct--metadata (addr b) free)
-     (free (field a-2 yet-another-name)))
+      my-struct--metadata (addr b) free))
 
     (scope ;; Test errors
      (var read-struct my-struct (array 0))
@@ -1948,6 +1953,4 @@
       (free-introspect-struct-fields
        my-struct--metadata (addr read-struct) free)))
 
-    (free (field a yet-another-name))
-
     (return 0))))