diff: skip test if seek is not possible on OS/2 kLIBC

This fixes the problem that 'diff - file' and 'cat file | diff - file'
fail due to a seek failure with a message 'diff.exe: -: Invalid seek',
because seek does not work on stdin and a pipe on OS/2 kLIBC.

* src/io.c (sip): Set skip_test to true if seek is not possible on
OS/2 kLIBC.

Author: komh

src/io.c

@@ -108,6 +108,13 @@ sip (struct file_data *current, bool skip_test)
 				     PTRDIFF_MAX - 2 * sizeof (word));
       current->buffer = xmalloc (current->bufsize);
 
+#ifdef __KLIBC__
+      /* Skip test if seek is not possible */
+      skip_test = skip_test
+		  || (lseek (current->desc, 0, SEEK_CUR) < 0
+		      && errno == ESPIPE);
+#endif
+
       if (! skip_test)
 	{
 	  /* Check first part of file to see if it's a binary file.  */