#81026: Perl binary no longer relocatable

#81026: Perl binary no longer relocatable

Provide a preprocessor macro PERL_RELOCATABLE_INCPUSH to tell
incpush_use_sep() to ignore the passed in len argument.  This
enables relocatable Perl distributions that patch the various
paths at install time.

Core Perl neither provides actual relocation scripts/programs,
nor endorses this practise as being "supported"; this patch
only makes it possible to create such tools.  It is therefore
undocumented outside the source level comments.