build: update gnulib submodule to latest

* src/merge.c (compute_changes): The TOO_EXPENSIVE heuristic in diffseq has
been removed, including compareseq's find_minimal parameter and the context's
too_expensive limit.  Adjust.
savebuf/savestr error handling

* src/patch.c (get_some_switches): The function savebuf (and therefore savestr)
copies strings using malloc.  If malloc fails, NULL is returned.  This is
intentional behavior so that in case of failure during "plan a" patching, "plan
b" can step in.  The return value has to be properly checked for NULL.  If the
return value must not be NULL, use xstrdup instead.
More savebuf/savestr error handling

* bootstrap.conf: use xmemdup0 module.
* src/pch.c (there_is_another_patch): Use xmemdup0 instead of savebuf when we
cannot recover from out-of-memory situations.
(intuit_diff_type): Likewise, use xstrdup instead of savestr.
(another_hunk): Handle the case when savestr returns NULL.
* src/util.c (fetchname, parse_name): Use xmemdup0 instead of savebuf when we
cannot recover from out-of-memory situations.

Bugs pointed out by Tobias Stoeckmann <tobias@stoeckmann.org>.
Add line number overflow checking

* bootstrap.conf: use intprops module.
* src/common.h: Define LINENUM_MIN and LINENUM_MAX macros.
* src/pch.c (another_hunk): Add line number overflow checking.  Based on Robert
C. Seacord's INT32-C document for integer overflow checking and Tobias
Stoeckmann's "integer overflows and oob memory access" patch for FreeBSD.