Now that I have a working Mac OS X setup, added the initial groundwork for the OS X port. This C file works correctly on both amd64 and i386 with clang [-m32] runtimetest.c -lobjc -framework Foundation; it will be converted to Go now.

darwintest/runtimetest.c

@@ -0,0 +1,22 @@
+// 27 february 2014
+#include <stdio.h>
+#include <objc/message.h>
+#include <objc/objc.h>
+#include <objc/runtime.h>
+
+int main(void)
+{
+	id NSString = objc_getClass("NSString");
+	SEL stringFromUTF8String =
+		sel_getUid("stringWithUTF8String:");
+	id str = objc_msgSend(NSString,
+		stringFromUTF8String,
+		"hello, world\n");
+	SEL UTF8String =
+		sel_getUid("UTF8String");
+
+	printf("%s",
+		(char *) objc_msgSend(str,
+			UTF8String));
+	return 0;
+}