[Linux] jsig is limited to a maximum of 64 signals

The jsig signal-interposition library is used to intercept signal management code to allow handlers to be chained such that the VM handlers and external program handlers for the same signal can work in cooperation.

On most "mainstream" Linux distributions the possible signal values range from 1 to 32 or 64. jsig accommodates this by using a 64-bit variable as a bit-mask.

Some implementations of Linux as reported here:

http://mail.openjdk.java.net/pipermail/hotspot-dev/2016-December/025416.html

have more than 64 signals and jsig can not be built on those platforms.

A better solution, as used by the AIX implementation of jsig, is to use a standard sigset_t to hold the signal values. In fact we may be able to consolidate and have a single POSIX version of jsig that is shared across most platforms.