Suppress -arch switches in the output of ExtUtils::Embed.

We previously found out that OS X's standard perl installation tries to put
-arch switches into Perl link commands, evidently in hopes of building
universal binaries.  But it doesn't work to add such switches in plperl's
link step if they weren't being used earlier, so this is basically
unworkable.  When using gcc the result is only some warnings; but LLVM
fails entirely, so this issue isn't as cosmetic as we originally thought.
Hence, back-patch commit d69a419e68 into
pre-9.0 branches.

config/perl.m4

@@ -25,12 +25,16 @@ AC_DEFUN([PGAC_CHECK_PERL_CONFIGS],
 
 # PGAC_CHECK_PERL_EMBED_LDFLAGS
 # -----------------------------
+# We are after Embed's ldopts, but without the subset mentioned in
+# Config's ccdlflags; and also without any -arch flags, which recent
+# Apple releases put in unhelpfully.  (If you want a multiarch build
+# you'd better be specifying it in more places than plperl's final link.)
 AC_DEFUN([PGAC_CHECK_PERL_EMBED_LDFLAGS],
 [AC_REQUIRE([PGAC_PATH_PERL])
 AC_MSG_CHECKING(for flags to link embedded Perl)
 pgac_tmp1=`$PERL -MExtUtils::Embed -e ldopts`
 pgac_tmp2=`$PERL -MConfig -e 'print $Config{ccdlflags}'`
-perl_embed_ldflags=`echo X"$pgac_tmp1" | sed "s/^X//;s%$pgac_tmp2%%"`
+perl_embed_ldflags=`echo X"$pgac_tmp1" | sed -e "s/^X//" -e "s%$pgac_tmp2%%" -e ["s/ -arch [-a-zA-Z0-9_]*//g"]`
 AC_SUBST(perl_embed_ldflags)dnl
 if test -z "$perl_embed_ldflags" ; then
 	AC_MSG_RESULT(no)

configure

@@ -4955,7 +4955,7 @@ echo "$as_me:$LINENO: checking for flags to link embedded Perl" >&5
 echo $ECHO_N "checking for flags to link embedded Perl... $ECHO_C" >&6
 pgac_tmp1=`$PERL -MExtUtils::Embed -e ldopts`
 pgac_tmp2=`$PERL -MConfig -e 'print $Config{ccdlflags}'`
-perl_embed_ldflags=`echo X"$pgac_tmp1" | sed "s/^X//;s%$pgac_tmp2%%"`
+perl_embed_ldflags=`echo X"$pgac_tmp1" | sed -e "s/^X//" -e "s%$pgac_tmp2%%" -e "s/ -arch [-a-zA-Z0-9_]*//g"`
 if test -z "$perl_embed_ldflags" ; then
 	echo "$as_me:$LINENO: result: no" >&5
 echo "${ECHO_T}no" >&6