Make configure check for IPC::Run when --enable-tap-tests is specified.

The TAP tests mostly don't work without IPC::Run, and the reason for
the failure is not immediately obvious from the error messages you get.
So teach configure to reject --enable-tap-tests unless IPC::Run exists.
Mostly this just involves adding ax_prog_perl_modules.m4 from the GNU
autoconf archives.

This was discussed last year, but we held off on the theory that we might
be switching to CMake soon.  That's evidently not happening for v10,
so let's absorb this now.

Eugene Kazakov and Michael Paquier

Discussion: https://postgr.es/m/56BDDC20.9020506@postgrespro.ru
Discussion: https://postgr.es/m/CAB7nPqRVKG_CR4Dy_AMfE6DXcr6F7ygy2goa2atJU4XkerDRUg@mail.gmail.com

aclocal.m4

@@ -1,5 +1,6 @@
 dnl aclocal.m4
 m4_include([config/ac_func_accept_argtypes.m4])
+m4_include([config/ax_prog_perl_modules.m4])
 m4_include([config/ax_pthread.m4])
 m4_include([config/c-compiler.m4])
 m4_include([config/c-library.m4])

config/ax_prog_perl_modules.m4

@@ -0,0 +1,77 @@
+# ===========================================================================
+#   https://www.gnu.org/software/autoconf-archive/ax_prog_perl_modules.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_PROG_PERL_MODULES([MODULES], [ACTION-IF-TRUE], [ACTION-IF-FALSE])
+#
+# DESCRIPTION
+#
+#   Checks to see if the given perl modules are available. If true the shell
+#   commands in ACTION-IF-TRUE are executed. If not the shell commands in
+#   ACTION-IF-FALSE are run. Note if $PERL is not set (for example by
+#   calling AC_CHECK_PROG, or AC_PATH_PROG), AC_CHECK_PROG(PERL, perl, perl)
+#   will be run.
+#
+#   MODULES is a space separated list of module names. To check for a
+#   minimum version of a module, append the version number to the module
+#   name, separated by an equals sign.
+#
+#   Example:
+#
+#     AX_PROG_PERL_MODULES( Text::Wrap Net::LDAP=1.0.3, ,
+#                           AC_MSG_WARN(Need some Perl modules)
+#
+# LICENSE
+#
+#   Copyright (c) 2009 Dean Povey <povey@wedgetail.com>
+#
+#   Copying and distribution of this file, with or without modification, are
+#   permitted in any medium without royalty provided the copyright notice
+#   and this notice are preserved. This file is offered as-is, without any
+#   warranty.
+
+#serial 8
+
+AU_ALIAS([AC_PROG_PERL_MODULES], [AX_PROG_PERL_MODULES])
+AC_DEFUN([AX_PROG_PERL_MODULES],[dnl
+
+m4_define([ax_perl_modules])
+m4_foreach([ax_perl_module], m4_split(m4_normalize([$1])),
+	  [
+	   m4_append([ax_perl_modules],
+		     [']m4_bpatsubst(ax_perl_module,=,[ ])[' ])
+          ])
+
+# Make sure we have perl
+if test -z "$PERL"; then
+AC_CHECK_PROG(PERL,perl,perl)
+fi
+
+if test "x$PERL" != x; then
+  ax_perl_modules_failed=0
+  for ax_perl_module in ax_perl_modules; do
+    AC_MSG_CHECKING(for perl module $ax_perl_module)
+
+    # Would be nice to log result here, but can't rely on autoconf internals
+    $PERL -e "use $ax_perl_module; exit" > /dev/null 2>&1
+    if test $? -ne 0; then
+      AC_MSG_RESULT(no);
+      ax_perl_modules_failed=1
+   else
+      AC_MSG_RESULT(ok);
+    fi
+  done
+
+  # Run optional shell commands
+  if test "$ax_perl_modules_failed" = 0; then
+    :
+    $2
+  else
+    :
+    $3
+  fi
+else
+  AC_MSG_WARN(could not find perl)
+fi])dnl

configure

@@ -16245,6 +16245,84 @@ done
   if test -z "$PERL"; then
     as_fn_error $? "Perl not found" "$LINENO" 5
   fi
+  # Check for necessary modules
+
+
+
+
+
+
+# Make sure we have perl
+if test -z "$PERL"; then
+# Extract the first word of "perl", so it can be a program name with args.
+set dummy perl; ac_word=$2
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
+$as_echo_n "checking for $ac_word... " >&6; }
+if ${ac_cv_prog_PERL+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  if test -n "$PERL"; then
+  ac_cv_prog_PERL="$PERL" # Let the user override the test.
+else
+as_save_IFS=$IFS; IFS=$PATH_SEPARATOR
+for as_dir in $PATH
+do
+  IFS=$as_save_IFS
+  test -z "$as_dir" && as_dir=.
+    for ac_exec_ext in '' $ac_executable_extensions; do
+  if as_fn_executable_p "$as_dir/$ac_word$ac_exec_ext"; then
+    ac_cv_prog_PERL="perl"
+    $as_echo "$as_me:${as_lineno-$LINENO}: found $as_dir/$ac_word$ac_exec_ext" >&5
+    break 2
+  fi
+done
+  done
+IFS=$as_save_IFS
+
+fi
+fi
+PERL=$ac_cv_prog_PERL
+if test -n "$PERL"; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $PERL" >&5
+$as_echo "$PERL" >&6; }
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+
+fi
+
+if test "x$PERL" != x; then
+  ax_perl_modules_failed=0
+  for ax_perl_module in 'IPC::Run' ; do
+    { $as_echo "$as_me:${as_lineno-$LINENO}: checking for perl module $ax_perl_module" >&5
+$as_echo_n "checking for perl module $ax_perl_module... " >&6; }
+
+    # Would be nice to log result here, but can't rely on autoconf internals
+    $PERL -e "use $ax_perl_module; exit" > /dev/null 2>&1
+    if test $? -ne 0; then
+      { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; };
+      ax_perl_modules_failed=1
+   else
+      { $as_echo "$as_me:${as_lineno-$LINENO}: result: ok" >&5
+$as_echo "ok" >&6; };
+    fi
+  done
+
+  # Run optional shell commands
+  if test "$ax_perl_modules_failed" = 0; then
+    :
+
+  else
+    :
+    as_fn_error $? "Perl module IPC::Run is required to run TAP tests" "$LINENO" 5
+  fi
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: could not find perl" >&5
+$as_echo "$as_me: WARNING: could not find perl" >&2;}
+fi
 fi
 
 # Thread testing

configure.in

@@ -2135,6 +2135,9 @@ if test "$enable_tap_tests" = yes; then
   if test -z "$PERL"; then
     AC_MSG_ERROR([Perl not found])
   fi
+  # Check for necessary modules
+  AX_PROG_PERL_MODULES(IPC::Run, ,
+    AC_MSG_ERROR([Perl module IPC::Run is required to run TAP tests]))
 fi
 
 # Thread testing