simplify multi-threaded errno, eliminate useless function pointer

src/errno/__errno_location.c

-#include <errno.h>
-#include "libc.h"
+#include "pthread_impl.h"
 
 int *__errno_location(void)
 {
 	static int e;
-	if (libc.errno_location) return libc.errno_location();
+	if (libc.main_thread) return __pthread_self()->errno_ptr;
 	return &e;
 }

src/internal/libc.h

@@ -5,7 +5,7 @@
 #include <stdio.h>
 
 struct __libc {
-	int *(*errno_location)(void);
+	void *main_thread;
 	int threaded;
 	int canceldisable;
 	int (*atexit)(void (*)(void));
@@ -14,7 +14,6 @@ struct __libc {
 	volatile int threads_minus_1;
 	int ofl_lock;
 	FILE *ofl_head;
-	void *main_thread;
 };
 
 

src/thread/pthread_self.c

@@ -6,21 +6,16 @@ static struct pthread main_thread;
 static const void *dummy[1] = { 0 };
 weak_alias(dummy, __pthread_tsd_main);
 
-static int *errno_location()
-{
-	return __pthread_self()->errno_ptr;
-}
-
 static int init_main_thread()
 {
 	if (__set_thread_area(&main_thread) < 0) return -1;
 	main_thread.canceldisable = libc.canceldisable;
 	main_thread.tsd = (void **)__pthread_tsd_main;
-	main_thread.self = libc.main_thread = &main_thread;
 	main_thread.errno_ptr = __errno_location();
-	libc.errno_location = errno_location;
+	main_thread.self = &main_thread;
 	main_thread.tid = main_thread.pid = 
 		__syscall(SYS_set_tid_address, &main_thread.tid);
+	libc.main_thread = &main_thread;
 	return 0;
 }