build-sys: rewrite TLS detection

build-sys: rewrite TLS detection

 * use more robust tls.m4 from gcc project

   The old version (from util-linux-ng) used AC_TRY_COMPILE. That's
   wrong. We need to use AC_RUN_IFELSE to check that the result is
   link-able and executable.

   The new version also test it TLS really works in multi-thread
   applications.

 * we need to detect TLS usability for cross-compiling

 * this new version supports __thread keyword only, it seems that we
   needn't to care about anything other

Signed-off-by: Karel Zak <kzak@redhat.com>