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).

Alpine notes:
This patch is copied from Fedora.

--- a/src/pl/plperl/GNUmakefile
+++ b/src/pl/plperl/GNUmakefile
@@ -43,6 +43,9 @@
 
 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) --load-extension=plperl  --load-extension=plperlu
 REGRESS = plperl plperl_lc plperl_trigger plperl_shared plperl_elog plperl_util plperl_init plperlu plperl_array
 # if Perl can support two interpreters in one backend,