Make filename hashing compatible with self contained builds (bug#43532)

Make filename hashing compatible with self contained builds (bug#43532)

	* Makefile.in (lispdirrel): Add replace template.
	(epaths-force): Form correctly 'PATH_REL_LOADSEARCH' into epath.h
	* configure.ac (lispdirrel): Define variable (relative path of the
	lisp files from the installation directory).
	* src/comp.c (Fcomp_el_to_eln_filename): Update algorithm not to
	rely on 'PATH_DUMPLOADSEARCH' but on 'PATH_REL_LOADSEARCH'.
	* src/epaths.in (PATH_REL_LOADSEARCH): Add macro template.