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.

Author: adunstan

config/perl.m4

@@ -1,4 +1,4 @@
-# $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