[NetworkManager-pptp/lr/ci: 3/5] build: file is required by configure

[Francesco Giudici <fgiudici src gnome org>]

commit 0d27794bf8a713ef7fdefaeb07ce856424ee899d
Author: Lubomir Rintel <lkundrak v3 sk>
Date:   Tue May 29 10:34:21 2018 +0200

    build: file is required by configure
    
    It's a not necessarily present among the packages in a minimal
    installation (such as Fedora's docker image). Worse even, configure just
    ends up passing wrong linker flags on some architectures, without a word
    of complain.
    
    Don't assume it's there.

 configure.ac | 5 +++++
 1 file changed, 5 insertions(+)
---
diff --git a/configure.ac b/configure.ac
index 6a9469b..7c7cd89 100644
--- a/configure.ac
+++ b/configure.ac
@@ -21,6 +21,11 @@ AC_PROG_INSTALL
 AC_PROG_LIBTOOL
 AC_PATH_PROG(GLIB_COMPILE_RESOURCES, glib-compile-resources)
 
+AC_CHECK_PROG([has_file], file, yes, no)
+if test x$has_file = xno ; then
+    AC_MSG_ERROR(["file" utility not found.])
+fi
+
 dnl
 dnl Required headers
 dnl