Remove sv_sigtbl from the arm64 sendsig().

[kib]

Summary

sv_sendsig is rather dubious idea. In essence, it was supposed to provide signal number translation table for standard sendsig() function. A fatal flaw is that sendsig() enforces the FreeBSD' ABI signal frame layout, which is wrong for ABI emulators. Since ABI emulators must form their own signal frames, they can easily transalte FreeBSD signal number into the ABI signal number, without exporting it in the sysentvec.

I doubt that arm64 has any ABI emulator at all.

Current plan is to fix misuse of the FreeBSD signal frame in the iBCS2 emulator and remove sv_sigtbl at all.

[andrew]

Would it pay to add a KASSERT for p->p_sysent->sv_sigtbl == NULL, or is the removal of sv_sigtbl planned for soon enough for this not to matter?

[kib]

In D2889#56733, @andrew wrote:

Would it pay to add a KASSERT for p->p_sysent->sv_sigtbl == NULL, or is the removal of sv_sigtbl planned for soon enough for this not to matter?

The goal is to remove sv_sigtbl.

How fast it happens, depends on how fast I get an approval to commit the iBCS2 changes.