libglib2: add patch to rework clock_gettime() test

libglib2: add patch to rework clock_gettime() test

The test for clock_gettime() in configure.in doesn't work properly
when a previous package has loaded the shared configuration cache with
informations about the availability of clock_gettime. A package such
as ctorrent does so, which means that compiling ctorrent *then*
libglib2 currently fails.

According to people on the Autoconf mailing list, the libglib2 test is
likely the one that needs to be fixed. The problem is that the
AC_CHECK_FUNCS() test assumes that if it finds clock_gettime() it
means that there's no need to add any -lrt flag to the
build. Unfortunately, due to the shared configuration cache, this test
is already done with -lrt, so the test succeeds, and libglib2 does not
know that it needs to add -lrt to G_THREAD_LIBS and
G_THREAD_LIBS_FOR_GTHREAD.

So instead, we remplace the test with an AC_SEARCH_LIBS() test,
followed by a test on the result of this AC_SEARCH_LIBS() test to add
the necessary -lrt to G_THREAD_LIBS and
G_THREAD_LIBS_FOR_GTHREAD. Therefore, even if the result for the
AC_SEARCH_LIBS() test is cached due to the prior execution ctorrent
./configure script, libglib2 ./configure will properly add -lrt to the
appropriate variables.

Obviously, as this patch modifies the configure.in file, we enable the
autoreconf step for the libglib2 package.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>