configure: search for lib with clock_getres()

Like clock_gettime(), clock_getres() is in -lrt for glibc < 2.17.
Add a check for it, like is done for clock_gettime().

Fixes:
    http://autobuild.buildroot.net/results/bce/bcecdbbce4a99eb1e9bfbf519857bf94d8952037/

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Reviewed-by: Quentin Glidic <sardemff7+git@sardemff7.net>

Makefile.am

@@ -190,6 +190,7 @@ weston_CFLAGS = $(AM_CFLAGS) $(COMPOSITOR_CFLAGS) $(LIBUNWIND_CFLAGS)
 weston_LDADD = libshared.la libweston-@LIBWESTON_MAJOR@.la \
 	$(COMPOSITOR_LIBS) $(LIBUNWIND_LIBS) \
 	$(DLOPEN_LIBS) $(LIBINPUT_BACKEND_LIBS) \
+	$(CLOCK_GETRES_LIBS) \
 	-lm
 
 weston_SOURCES = 					\

configure.ac

@@ -88,8 +88,9 @@ PKG_PROG_PKG_CONFIG()
 
 WESTON_SEARCH_LIBS([DLOPEN], [dl], [dlopen])
 
-# In old glibc versions (< 2.17) clock_gettime() is in librt
+# In old glibc versions (< 2.17) clock_gettime() and clock_getres() are in librt
 WESTON_SEARCH_LIBS([CLOCK_GETTIME], [rt], [clock_gettime])
+WESTON_SEARCH_LIBS([CLOCK_GETRES], [rt], [clock_getres])
 
 AC_CHECK_DECL(SFD_CLOEXEC,[],
 	      [AC_MSG_ERROR("SFD_CLOEXEC is needed to compile weston")],