Apparently Windows doesn't have strndup or index.

mach/proto/mcg/main.c

@@ -15,7 +15,7 @@ bool tracing(char k)
     if (!tracechars)
         return false;
 
-    return index(tracechars, k);
+    return strchr(tracechars, k);
 }
 
 void tracef(char k, const char* fmt, ...)

mach/proto/mcg/mcg.h

@@ -9,6 +9,7 @@
 #include <string.h>
 #include <assert.h>
 #include <errno.h>
+#include "system.h"
 #include "em_arith.h"
 #include "em_label.h"
 #include "em.h"

modules/src/system/strndup.c

@@ -0,0 +1,19 @@
+#include <stdlib.h>
+#include <string.h>
+#include "system.h"
+
+#if defined WIN32
+/* Really? */
+char* strndup(const char* s, size_t n)
+{
+    size_t len = strnlen(s, n);
+    char* ns = malloc(len + 1);
+    if (!ns)
+        return NULL;
+
+    ns[len] = '\0';
+    memcpy(ns, s, len);
+    return ns;
+}
+#endif
+

modules/src/system/system.h

@@ -84,4 +84,9 @@ void sys_basename(const char *str, register char *dst);
  * the same semantics as ISO C90 tmpnam() */
 char* sys_tmpnam(char *buffer);
 
+#if defined WIN32
+/* Really? */
+extern char* strndup(const char* s, size_t n);
+#endif
+
 #endif /* __SYSTEM_INCLUDED__ */