Test linking libperl.so using only Perl's required libraries.

It appears that perl_embed_ldflags should already mention all the libraries
that are required by libperl.so itself.  So let's try the test link with
just those and not the other LIBS we've found up to now.  This should
more nearly reproduce what will happen when plperl is linked, and perhaps
will fix buildfarm member okapi's problem.

configure

@@ -29187,7 +29187,7 @@ fi
   # this writing Debian packages them separately.  There is no known reason to
   # waste cycles on separate probes for the Tcl or Python libraries, though.
   pgac_save_LIBS=$LIBS
-  LIBS="$perl_embed_ldflags $LIBS"
+  LIBS="$perl_embed_ldflags"
   { $as_echo "$as_me:$LINENO: checking for libperl" >&5
 $as_echo_n "checking for libperl... " >&6; }
   cat >conftest.$ac_ext <<_ACEOF

configure.in

@@ -1803,7 +1803,7 @@ if test "$with_perl" = yes; then
   # this writing Debian packages them separately.  There is no known reason to
   # waste cycles on separate probes for the Tcl or Python libraries, though.
   pgac_save_LIBS=$LIBS
-  LIBS="$perl_embed_ldflags $LIBS"
+  LIBS="$perl_embed_ldflags"
   AC_MSG_CHECKING([for libperl])
   AC_TRY_LINK([
 #include <EXTERN.h>