stdlib: Sync canonicalize with gnulib [BZ #10635] [BZ #26592] [BZ #26341] [BZ #24970]

It sync with gnulib version ae9fb3d66.  The testcase for BZ#23741
(stdlib/test-bz22786.c) is adjusted to check also for ENOMEM.

The patch fixes multiple realpath issues:

  - Portability fixes for errno clobbering on free (BZ#10635).  The
    function does not call free directly anymore, although it might be
    done through scratch_buffer_free.  The free errno clobbering is
    being tracked by BZ#17924.

  - Pointer arithmetic overflows in realpath (BZ#26592).

  - Realpath cyclically call __alloca(path_max) to consume too much
    stack space (BZ#26341).

  - Realpath mishandles EOVERFLOW; stat not needed anyway (BZ#24970).
    The check is done through faccessat now.

Checked on x86_64-linux-gnu and i686-linux-gnu.