Detect and error out on inability to get proper linkage information required...

Detect and error out on inability to get proper linkage information required for plperl, usually due to absence of perl ExtUtils::Embed module. Backpatch as far as 8.1.

config/perl.m4

-# $PostgreSQL: pgsql/config/perl.m4,v 1.3 2003/11/29 19:51:17 pgsql Exp $
+# $PostgreSQL: pgsql/config/perl.m4,v 1.4 2008/11/12 00:00:05 adunstan Exp $
 
 
 # PGAC_PATH_PERL
@@ -32,4 +32,12 @@ 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%$pgac_tmp2%%"`
 AC_SUBST(perl_embed_ldflags)dnl
-AC_MSG_RESULT([$perl_embed_ldflags])])
+if test -z "$perl_embed_ldflags" ; then
+	AC_MSG_RESULT(no)
+	AC_MSG_ERROR([could not determine flags for linking embedded Perl.
+This probably means that ExtUtils::Embed or ExtUtils::MakeMaker is not
+installed.])
+else
+	AC_MSG_RESULT([$perl_embed_ldflags])
+fi
+])# PGAC_CHECK_PERL_EMBED_LDFLAGS

configure

@@ -6420,10 +6420,23 @@ 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%$pgac_tmp2%%"`
-{ echo "$as_me:$LINENO: result: $perl_embed_ldflags" >&5
+if test -z "$perl_embed_ldflags" ; then
+	{ echo "$as_me:$LINENO: result: no" >&5
+echo "${ECHO_T}no" >&6; }
+	{ { echo "$as_me:$LINENO: error: could not determine flags for linking embedded Perl.
+This probably means that ExtUtils::Embed or ExtUtils::MakeMaker is not
+installed." >&5
+echo "$as_me: error: could not determine flags for linking embedded Perl.
+This probably means that ExtUtils::Embed or ExtUtils::MakeMaker is not
+installed." >&2;}
+   { (exit 1); exit 1; }; }
+else
+	{ echo "$as_me:$LINENO: result: $perl_embed_ldflags" >&5
 echo "${ECHO_T}$perl_embed_ldflags" >&6; }
 fi
 
+fi
+
 if test "$with_python" = yes; then
   # Extract the first word of "python", so it can be a program name with args.
 set dummy python; ac_word=$2