Import strtok_r gnulib module

Import strtok_r gnulib module

gdb/linux-tdep.c recently gained a strtok_r use.  That broke
--enable-targets=all with some versions of mingw64, which don't have
strtok_r:

  https://sourceware.org/ml/gdb-patches/2015-04/msg00266.html

Fix that by importing the strtok_r gnulib module.

gdb/ChangeLog:
2015-04-09  Pedro Alves  <palves@redhat.com>

	* gnulib/update-gnulib.sh (IMPORTED_GNULIB_MODULES): Add strtok_r.
	* gnulib/Makefile.in (aclocal_m4_deps): Add import/m4/strtok_r.m4.
	* gnulib/configure, gnulib/config.in, gnulib/aclocal.m4: Regenerate.
	* gnulib/import/Makefile.am: Update.
	* gnulib/import/Makefile.in: Update.
	* gnulib/import/m4/gnulib-cache.m4: Update.
	* gnulib/import/m4/gnulib-comp.m4: Update.
	* gnulib/import/m4/strtok_r.m4: New file.
	* gnulib/import/strtok_r.c: New file.