Make libkms build default OS-dependent

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
diff --git a/configure.ac b/configure.ac
index fcfd07b..3794838 100644
--- a/configure.ac
+++ b/configure.ac
@@ -46,8 +46,8 @@
 
 AC_ARG_ENABLE(libkms,
 	      AS_HELP_STRING([--disable-libkms],
-	      [Disable KMS mm abstraction library (default: enabled)]),
-	      [LIBKMS=$enableval], [LIBKMS=yes])
+	      [Disable KMS mm abstraction library (default: auto)]),
+	      [LIBKMS=$enableval], [LIBKMS=auto])
 
 AC_ARG_ENABLE(intel,
 	      AS_HELP_STRING([--disable-intel],
@@ -146,6 +146,14 @@
 	AC_DEFINE(UDEV, 1, [Have UDEV support])
 fi
 
+AC_CANONICAL_HOST
+if test "x$LIBKMS" = xauto ; then
+	case $host_os in
+		linux*)		LIBKMS="yes" ;;
+		*)		LIBKMS="no" ;;
+	esac
+fi
+
 AM_CONDITIONAL(HAVE_LIBKMS, [test "x$LIBKMS" = xyes])
 
 AM_CONDITIONAL(HAVE_VMWGFX, [test "x$VMWGFX" = xyes])