libio: Implement internal function __libc_readline_unlocked

This is a variant of fgets which fails with ERANGE if the
buffer is too small, and the buffer length is given as an
argument of type size_t.

This function will be useful for implementing NSS file reading
operations.  Compared to a direct implementation using the public API,
it avoids an lseek system call in case the line terminator can be
found in the internal read buffer.

libio/fseeko.c

@@ -24,11 +24,15 @@
    This exception applies to code released by its copyright holders
    in files containing the exception.  */
 
+/* We need to disable the redirect for __fseeko64 for the alias
+   definitions below to work.  */
+#define __fseeko64 __fseeko64_disable
+
 #include "libioP.h"
 #include "stdio.h"
 
 int
-fseeko (FILE *fp, off_t offset, int whence)
+__fseeko (FILE *fp, off_t offset, int whence)
 {
   int result;
   CHECK_FILE (fp, -1);
@@ -37,7 +41,11 @@ fseeko (FILE *fp, off_t offset, int whence)
   _IO_release_lock (fp);
   return result;
 }
+weak_alias (__fseeko, fseeko)
 
 #ifdef __OFF_T_MATCHES_OFF64_T
-weak_alias (fseeko, fseeko64)
+weak_alias (__fseeko, fseeko64)
+# undef __fseeko64
+strong_alias (__fseeko, __fseeko64)
+libc_hidden_ver (__fseeko, __fseeko64)
 #endif