libsigsegv: disable test suite to avoid crashes with certain kernel versions

Further details are at:

 - https://lists.gnu.org/archive/html/bug-libsigsegv/2015-01/msg00001.html
 - http://lists.opensuse.org/opensuse-factory/2015-01/msg00408.html

Resolves https://github.com/NixOS/nixpkgs/issues/6028, kind of.