configure: check for clock_gettime and the providing library

clock_gettime is provided by -lrt so we must check for it.

Fixes build issues like observed in Buildroot;
    http://autobuild.buildroot.org/results/9df/9df2c09963b97524621f8323b279b8a1672d4b6c/build-end.log

Signed-off-by: "Yann E. MORIN" <[email protected]>

Author: yann-morin-1998

configure.ac

@@ -16,6 +16,8 @@ AC_PROG_CC
 # Checks for libraries.
 AC_CHECK_LIB([jpeg], [jpeg_start_compress])
 AC_CHECK_LIB([v4l2], [v4l2_open])
+AC_SEARCH_LIBS([clock_gettime],[rt],,
+               [AC_MSG_ERROR([no library contains clock_gettime])])
 
 # Checks for header files.
 AC_CHECK_HEADERS([fcntl.h malloc.h stdlib.h string.h sys/ioctl.h sys/time.h unistd.h])
@@ -26,5 +28,6 @@ AC_TYPE_SIZE_T
 # Checks for library functions.
 AC_FUNC_MALLOC
 AC_CHECK_FUNCS([getpagesize select strerror])
+AC_CHECK_FUNCS([clock_gettime])
 
 AC_OUTPUT