Expose public garbage collector API for C language

You can now do epic things like this:

    puts(_gc(xasprintf("%d", 123)));

The _gc() API is shorthand for _defer() which works like Go's keyword:

    const char *s = xasprintf("%d", 123);
    _defer(free, s);
    puts(s);

Be sure to always use -fno-omit-frame-pointer which makes code fast too.

Enjoy! See also #114

libc/runtime/print.greg.c

@@ -34,10 +34,10 @@ static void __sys_print_nt(const void *data, size_t len) {
   int64_t hand;
   char xmm[256];
   uint32_t wrote;
-  savexmm(xmm + 128);
+  _savexmm(xmm + 128);
   hand = __imp_GetStdHandle(kNtStdErrorHandle);
   __imp_WriteFile(hand, data, len, &wrote, NULL);
-  loadxmm(xmm + 128);
+  _loadxmm(xmm + 128);
 }
 
 /**