Import strchrnul from gnulib and use it

Import strchrnul from gnulib and use it

For a forthcoming patch, I need a "skip_to_colon" function.  I noticed
there are two skip_to_semicolon (one in gdb and one in gdbserver). I
thought we could put it in common/, and generalize it for any character.
It turns out that the strchrnul function does exactly that.  I imported
the corresponding module from gnulib, for those systems that do not have
it.

There are probably more places where this function can be used instead
of doing the work by hand (I am looking at
remote-utils.c::look_up_one_symbol).

gdb/ChangeLog:

	* remote.c (skip_to_semicolon): Remove.
	(remote_parse_stop_reply): Use strchrnul instead of
	skip_to_semicolon.
	* gnulib/update-gnulib.sh (IMPORTED_GNULIB_MODULES): Add
	strchrnul.
	* gnulib/aclocal.m4: Regenerate.
	* gnulib/config.in: Regenerate.
	* gnulib/configure: Regenerate.
	* gnulib/import/Makefile.am: Regenerate.
	* gnulib/import/Makefile.in: Regenerate.
	* gnulib/import/m4/gnulib-cache.m4: Regenerate.
	* gnulib/import/m4/gnulib-comp.m4: Regenerate.
	* gnulib/import/m4/rawmemchr.m4: New file.
	* gnulib/import/m4/strchrnul.m4: New file.
	* gnulib/import/rawmemchr.c: New file.
	* gnulib/import/rawmemchr.valgrind: New file.
	* gnulib/import/strchrnul.c: New file.
	* gnulib/import/strchrnul.valgrind: New file.

gdb/gdbserver/ChangeLog:

	* server.c (skip_to_semicolon):  Remove.
	(process_point_options): Use strchrnul instead of
	skip_to_semicolon.