We configure Postgres with --disable-rpath because for the most part we
want to leave it to ldconfig to determine where libraries are.  However,
for some reason the Perl package puts libperl.so in a nonstandard place
and doesn't add that place to the ldconfig search path.  I think this
is a Perl packaging bug, myself, but apparently it's not going to change.
So work around it by adding an rpath spec to plperl.so (only).
Per bug #162198.

diff -up postgresql-13.1/src/pl/plperl/GNUmakefile.patch3 postgresql-13.1/src/pl/plperl/GNUmakefile
--- postgresql-13.1/src/pl/plperl/GNUmakefile.patch3	2020-12-09 21:29:47.269556344 +0100
+++ postgresql-13.1/src/pl/plperl/GNUmakefile	2020-12-09 21:31:06.100395606 +0100
@@ -55,6 +55,9 @@ endif # win32
 
 SHLIB_LINK = $(perl_embed_ldflags)
 
+# Force rpath to be used even though we disable it everywhere else
+SHLIB_LINK += $(rpath)
+
 REGRESS_OPTS = --dbname=$(PL_TESTDB)
 REGRESS = plperl_setup plperl plperl_lc plperl_trigger plperl_shared \
 	plperl_elog plperl_util plperl_init plperlu plperl_array \