build-sys: disable NLS support if intltool is not found

IT_PROG_INTLTOOL makes configure fail if intltool is not present.  If we can
not find intltool, then disable NLS (otherwise make in po/ fails since MSGFMT
will not be defined.)

Tested: Built it on a host without intltool.
  $ ./configure --enable-nls
  ...
  checking for intltool-merge... no
  configure: error: --enable-nls requested but intltool not found

  $ ./configure --disable-polkit
  ...
  checking for intltool-merge... no
  configure: WARNING: *** Disabling NLS support because intltool was not found
  checking whether NLS is requested... no
  ...
  $ make

https://bugs.freedesktop.org/show_bug.cgi?id=79692

1 files changed, 12 insertions, 0 deletions

diff --git a/configure.ac b/configure.ac
index 31879d3fb4..93aba06739 100644
--- a/configure.ac
+++ b/configure.ac
@@ -49,6 +49,18 @@ AS_IF([test "x$enable_static" = "xyes"], [AC_MSG_ERROR([--enable-static is not s
 AS_IF([test "x$enable_largefile" = "xno"], [AC_MSG_ERROR([--disable-largefile is not supported by systemd])])
 
 # i18n stuff for the PolicyKit policy files
+
+# Check whether intltool can be found, disable NLS otherwise
+AC_CHECK_PROG(intltool_found, [intltool-merge], [yes], [no])
+AS_IF([test x"$intltool_found" != xyes],
+      [AS_IF([test x"$enable_nls" = xyes],
+             [AC_MSG_ERROR([--enable-nls requested but intltool not found])],
+             [AS_IF([test x"$enable_nls" != xno],
+                    [AC_MSG_WARN([*** Disabling NLS support because intltool was not found])
+                     enable_nls=no])
+             ])
+      ])
+
 AM_NLS
 AS_IF([test x"$enable_nls" != xno], [
     # intltoolize greps for '^(AC|IT)_PROG_INTLTOOL', so it needs to be on its own line