x-to-1: avoid failure due to missing perl modules

[Bruno Haible]

Building gettext on OpenBSD 6.3, I get this failure:

Updating man page gettext.1.in
/usr/bin/perl -w -- ../../../gettext-runtime/man/help2man 
--include=../../../gettext-runtime/man/gettext.x ../src/gettext > gettext.1.in
Can't locate Locale/gettext.pm in @INC (you may need to install the 
Locale::gettext module) (@INC contains: 
/usr/local/libdata/perl5/site_perl/amd64-openbsd 
/usr/local/libdata/perl5/site_perl /usr/libdata/perl5/amd64-openbsd 
/usr/libdata/perl5 .) at ../../../gettext-runtime/man/help2man line 29.
BEGIN failed--compilation aborted at ../../../gettext-runtime/man/help2man line 
29.
*** Error 1 in gettext-runtime/man (Makefile:1660 'gettext.1.in')

This patch avoids the failure, leading to a message
"WARNING: The man page gettext.1.in cannot be updated yet."
- and the build continues.


2019-04-13  Bruno Haible  <address@hidden>

        x-to-1: Avoid failure due to missing perl modules.
        * build-aux/x-to-1.in: Test whether all the perl modules that help2man
        needs are installed.

diff --git a/build-aux/x-to-1.in b/build-aux/x-to-1.in
index 1b09d33..b31175f 100644
--- a/build-aux/x-to-1.in
+++ b/build-aux/x-to-1.in
@@ -41,7 +41,20 @@ aux="$4"
 output="$5"
 
 progname=`basename $aux .x`
-case "$PERL" in *"/missing perl") perlok=no;; *) perlok=yes;; esac
+# configure determined whether perl exists.
+case "$PERL" in
+  *"/missing perl")
+    perlok=no
+    ;;
+  *)
+    # Determine whether all the perl modules that help2man needs are installed.
+    if $PERL $HELP2MAN --help >/dev/null 2>/dev/null; then
+      perlok=yes
+    else
+      perlok=no
+    fi
+    ;;
+esac
 if test @CROSS_COMPILING@ = no && test -f $executable && test $perlok = yes; 
then
   echo "Updating man page $output"
   echo "$PERL $HELP2MAN --include=$aux $executable > $output"