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

[Lubomir Rintel <lkundrak src gnome org>]

commit 890508c10e7b28c752aeb83d385ccbd1b21aee44
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 baea8ec..13531e2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -30,6 +30,11 @@ AC_PROG_LIBTOOL
 AC_PROG_LN_S
 AC_PROG_MKDIR_P
 
+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