debuginfod: Make sure PATH_MAX exists in debuginfod-client.c

debuginfod: Make sure PATH_MAX exists in debuginfod-client.c

Some systems (Hurd) don't define PATH_MAX (which is optional according
to POSIX). Make sure it is defined and no special linux specific
headers are used in debuginfod-client.c.

	* debuginfod/debuginfod-client.c: Include limits.h instead of
	linux/limits. If PATH_MAX isn't define it to 4K (the default
	on GNU/Linux).

https://sourceware.org/bugzilla/show_bug.cgi?id=34016

Signed-off-by: Mark Wielaard <mark@klomp.org>