Port to older Solaris 10 versions (Bug#10677).

Port to older Solaris 10 versions (Bug#10677).

Bug reported by Chong Yidong for SunOS 5.10 Generic_127111-11 sparc.
I cannot reproduce it on SunOS 5.10 Generic_141444-09 sparc but
possibly this is because Sun fixed the 'stat' bug in my version.
* Makefile.in (GNULIB_TOOL_FLAGS): Do not avoid the pathmax module.
* lib/pathmax.h, m4/pathmax.m4: New files, from gnulib.
* lib/gnulib.mk, m4/gl-comp.m4: Regenerate.
These changes are based on gnulib version
4f11d6bebc3098c64ffde27079ab0d0cecfd0cdc dated 2011-10-07 20:59:10,
because Emacs is in feature freeze and we do not want to merge any
more-recent changes from gnulib.