Revert "newlib: fix fseek optimization with SEEK_CUR"

This reverts commit 59362c80e3.

This breaks gnulib's autoconf test for POSIX compatibility of
fflush/fseek.  After fflush/fseek, ftello and lseek are out of
sync, with lseek having the wrong offset.  This breaks backward
compatibility with Cygwin applications.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

newlib/libc/stdio/fseeko.c

@@ -141,12 +141,31 @@ _fseeko_r (struct _reent *ptr,
   switch (whence)
     {
     case SEEK_CUR:
-      curoff = _ftello_r(ptr, fp);
+      /*
-      if (curoff == -1L)
+       * In order to seek relative to the current stream offset,
-        {
+       * we have to first find the current stream offset a la
-          _newlib_flockfile_exit (fp);
+       * ftell (see ftell for details).
-          return EOF;
+       */
-        }
+      _fflush_r (ptr, fp);   /* may adjust seek offset on append stream */
+      if (fp->_flags & __SOFF)
+	curoff = fp->_offset;
+      else
+	{
+	  curoff = seekfn (ptr, fp->_cookie, (_fpos_t) 0, SEEK_CUR);
+	  if (curoff == -1L)
+	    {
+	      _newlib_flockfile_exit (fp);
+	      return EOF;
+	    }
+	}
+      if (fp->_flags & __SRD)
+	{
+	  curoff -= fp->_r;
+	  if (HASUB (fp))
+	    curoff -= fp->_ur;
+	}
+      else if (fp->_flags & __SWR && fp->_p != NULL)
+	curoff += fp->_p - fp->_bf._base;
 
       offset += curoff;
       whence = SEEK_SET;

newlib/libc/stdio64/fseeko64.c

@@ -142,12 +142,31 @@ _fseeko64_r (struct _reent *ptr,
   switch (whence)
     {
     case SEEK_CUR:
-      curoff = _ftello64_r(ptr, fp);
+      /*
-      if (curoff == -1L)
+       * In order to seek relative to the current stream offset,
-        {
+       * we have to first find the current stream offset a la
-          _newlib_flockfile_exit (fp);
+       * ftell (see ftell for details).
-          return EOF;
+       */
-        }
+      _fflush_r (ptr, fp);   /* may adjust seek offset on append stream */
+      if (fp->_flags & __SOFF)
+	curoff = fp->_offset;
+      else
+	{
+	  curoff = seekfn (ptr, fp->_cookie, (_fpos64_t) 0, SEEK_CUR);
+	  if (curoff == -1L)
+	    {
+	      _newlib_flockfile_exit(fp);
+	      return EOF;
+	    }
+	}
+      if (fp->_flags & __SRD)
+	{
+	  curoff -= fp->_r;
+	  if (HASUB (fp))
+	    curoff -= fp->_ur;
+	}
+      else if (fp->_flags & __SWR && fp->_p != NULL)
+	curoff += fp->_p - fp->_bf._base;
 
       offset += curoff;
       whence = SEEK_SET;