Fails to build on Debian hppa: uses non-standard sa_restorer field of struct sigaction

[jscott0]

Hi,

I'm forwarding this issue on behalf of a reporter in Debian. Since merging #656 it seems like there's a hard-coded assumption that systems other than macOS and the BSDs have the sa_restorer field, but we use the GNU C Library and it doesn't provide this for hppa at least.

KLayout should test at build time whether the field exists, or set only the fields specified by POSIX and allow the rest to be zeroed out (perhaps with designated initializers). Note that my Linux man page says

The sa_restorer field is not intended for application use.

[klayoutmatthias]

Thanks for reporting this issue.

I'll use a fetch-and-modify scheme to install the signal handlers to get rid of the #ifdefs and the OS dependencies.

Matthias