use namespace-safe __lseek for __stdio_seek instead of direct syscall

this probably saves a few bytes, avoids duplicating the clunky
lseek/_llseek syscall convention in two places, and sets the stage for
fixing broken seeks on x32 and mipsn32.

src/include/unistd.h

@@ -9,5 +9,6 @@ hidden int __dup3(int, int, int);
 hidden int __mkostemps(char *, int, int);
 hidden int __execvpe(const char *, char *const *, char *const *);
 hidden int __aio_close(int);
+hidden off_t __lseek(int, off_t, int);
 
 #endif

src/stdio/__stdio_seek.c

@@ -1,13 +1,7 @@
 #include "stdio_impl.h"
+#include <unistd.h>
 
 off_t __stdio_seek(FILE *f, off_t off, int whence)
 {
-	off_t ret;
-#ifdef SYS__llseek
-	if (syscall(SYS__llseek, f->fd, off>>32, off, &ret, whence)<0)
-		ret = -1;
-#else
-	ret = syscall(SYS_lseek, f->fd, off, whence);
-#endif
-	return ret;
+	return __lseek(f->fd, off, whence);
 }

src/unistd/lseek.c

@@ -1,7 +1,7 @@
 #include <unistd.h>
 #include "syscall.h"
 
-off_t lseek(int fd, off_t offset, int whence)
+off_t __lseek(int fd, off_t offset, int whence)
 {
 #ifdef SYS__llseek
 	off_t result;
@@ -11,4 +11,5 @@ off_t lseek(int fd, off_t offset, int whence)
 #endif
 }
 
-weak_alias(lseek, lseek64);
+weak_alias(__lseek, lseek);
+weak_alias(__lseek, lseek64);