Get GNU GMP test suite fully passing

- Fix stdio fmemopen() buffer behaviors
- Fix scanf() to return EOF when appropriate
- Prefer fseek/ftell names over fseeko/ftello
- Ensure locale field is always set in the TIB
- Fix recent regression in vfprintf() return count
- Make %n directive in scanf() have standard behavior

libc/thread/mktls.c

@@ -25,6 +25,7 @@
 #include "libc/mem/mem.h"
 #include "libc/runtime/internal.h"
 #include "libc/runtime/runtime.h"
+#include "libc/str/locale.h"
 #include "libc/str/str.h"
 #include "libc/thread/spawn.h"
 #include "libc/thread/tls.h"
@@ -41,6 +42,7 @@ static char *_mktls_finish(struct CosmoTib **out_tib, char *mem,
   tib->tib_ftrace = old->tib_ftrace;
   tib->tib_strace = old->tib_strace;
   tib->tib_sigmask = old->tib_sigmask;
+  tib->tib_locale = (intptr_t)&__c_dot_utf8_locale;
   atomic_store_explicit(&tib->tib_tid, -1, memory_order_relaxed);
   if (out_tib) {
     *out_tib = tib;