[grilo] build: Fix tests enablements

[Bastien Nocera <hadess src gnome org>]

commit a05a65f34ba36f44a3e06390c6806727f7454dfa
Author: Bastien Nocera <hadess hadess net>
Date:   Wed Sep 2 13:54:12 2015 +0200

    build: Fix tests enablements
    
    Spotted by Michael Terry <michael terry canonical com>
    
    https://bugzilla.gnome.org/show_bug.cgi?id=693450

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 5455099..8ed1730 100644
--- a/configure.ac
+++ b/configure.ac
@@ -240,7 +240,7 @@ AC_ARG_ENABLE([tests],
         AS_HELP_STRING([--enable-tests],[build unit tests]),
         enable_tests=yes)
 
-AM_CONDITIONAL(ENABLE_TESTS, test "enable_tests" = "xyes")
+AM_CONDITIONAL(ENABLE_TESTS, test "x$enable_tests" = "xyes")
 
 # ----------------------------------------------------------
 # GTK-DOC