v4l2src: link against -lrt for clock_gettime()

Need to explicitly link against -lrt for clock_gettime(), which
we don't get in the libs any more, because core moved the
gmodule-no-export-2.0 bit into Requires.Private.

Not required for newer glibc, but for older ones, so check for that.

configure.ac

@@ -134,6 +134,14 @@ dnl check for libm, for sin()
 LT_LIB_M
 AC_SUBST(LIBM)
 
+AC_CHECK_FUNCS(clock_gettime, [], [
+  AC_CHECK_LIB(rt, clock_gettime, [
+    AC_DEFINE(HAVE_CLOCK_GETTIME, 1)
+    LIBRT="-lrt"
+    AC_SUBST([LIBRT])
+  ])
+])
+
 dnl *** checks for header files ***
 
 dnl check if we have ANSI C header files

sys/v4l2/Makefile.am

@@ -64,7 +64,8 @@ libgstvideo4linux2_la_LIBADD =   $(GST_PLUGINS_BASE_LIBS) \
 				 $(GST_LIBS) \
 				 $(xv_libs) \
 				 $(LIBV4L2_LIBS) \
-				 $(GUDEV_LIBS)
+				 $(GUDEV_LIBS) \
+				 $(LIBRT)
 
 noinst_HEADERS = \
 	gstv4l2bufferpool.h \