[gnome-desktop] build: unbreak on OpenBSD

[Antoine Jacoutot <ajacoutot src gnome org>]

commit e6ba67b4de48db96a006829e9d326b06c9d4ba9f
Author: Antoine Jacoutot <ajacoutot gnome org>
Date:   Sat Apr 19 00:38:02 2014 +0200

    build: unbreak on OpenBSD
    
    On OpenBSD clock_gettime(2) is part of libc and there is not librt, so
    add an according check.

 configure.ac                 |    3 +++
 libgnome-desktop/Makefile.am |    4 +++-
 2 files changed, 6 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 530ff65..aaec075 100644
--- a/configure.ac
+++ b/configure.ac
@@ -127,6 +127,9 @@ AC_SUBST(XEXT_REQUIRED)
 AC_CHECK_LIBM
 AC_SUBST(LIBM)
 
+AC_CHECK_LIB([rt], [clock_gettime], [LIBRT="-lrt"], [LIBRT=""])
+AC_SUBST(LIBRT)
+
 dnl we need x11 for GnomeBG
 
 PKG_CHECK_MODULES(XLIB, x11,
diff --git a/libgnome-desktop/Makefile.am b/libgnome-desktop/Makefile.am
index 5305584..7eabb67 100644
--- a/libgnome-desktop/Makefile.am
+++ b/libgnome-desktop/Makefile.am
@@ -1,4 +1,5 @@
 CLEANFILES =
+NULL =
 
 EXTRA_DIST =
 noinst_LTLIBRARIES =
@@ -79,7 +80,8 @@ libgnome_desktop_3_la_LIBADD =        \
        $(LIBM)                 \
        $(GNOME_DESKTOP_LIBS)   \
        libgsystem.la           \
-       -lrt
+       $(LIBRT)                \
+       $(NULL)
 
 libgnome_desktop_3_la_LDFLAGS = \
        -version-info $(LT_VERSION) \