fixincludes: simplify handling for access() failure [PR21283, PR80047]

POSIX says:

    On some implementations, if buf is a null pointer, getcwd() may obtain
    size bytes of memory using malloc(). In this case, the pointer returned
    by getcwd() may be used as the argument in a subsequent call to free().
    Invoking getcwd() with buf as a null pointer is not recommended in
    conforming applications.

This produces an error building GCC with --enable-werror-always:

    ../../../fixincludes/fixincl.c: In function ‘process’:
    ../../../fixincludes/fixincl.c:1356:7: error: argument 1 is null but
    the corresponding size argument 2 value is 4096 [-Werror=nonnull]

It's suggested by POSIX to call getcwd() with progressively larger
buffers until it does not give an [ERANGE] error. However, it's highly
unlikely that this error-handling route is ever used.

So we can simplify it instead of writting too much code.  We give up to
use getcwd(), because `make` will output a `Leaving directory ...` message
containing the path to cwd when we call abort().

fixincludes/ChangeLog:

	PR other/21823
	PR bootstrap/80047
	* fixincl.c (process): Simplify the handling for highly
	  unlikely access() failure, to avoid using non-standard
	  extensions.

fixincludes/fixincl.c

@@ -1352,11 +1352,10 @@ process (void)
 
   if (access (pz_curr_file, R_OK) != 0)
     {
-      int erno = errno;
-      fprintf (stderr, "Cannot access %s from %s\n\terror %d (%s)\n",
-               pz_curr_file, getcwd ((char *) NULL, MAXPATHLEN),
-               erno, xstrerror (erno));
-      return;
+      /* Some really strange error happened.  */
+      fprintf (stderr, "Cannot access %s: %s\n", pz_curr_file,
+	       xstrerror (errno));
+      abort ();
     }
 
   pz_curr_data = load_file (pz_curr_file);