Add $OpenBSD$ tag and declare that this file is in the public domain.

requested by miod@

Enable support for floating-point exceptions. We always run in "precise"
mode. On modern processors (POWER8 and later) there is no performance
penalty for this as long as exceptions are disabled in

Enable support for floating-point exceptions. We always run in "precise"
mode. On modern processors (POWER8 and later) there is no performance
penalty for this as long as exceptions are disabled in the FPSCR (which
is the default). This way we don't have to implement an
architecture-dependent system call to set the mode, as it can only be done
by the kernel.

With help from gkoehler@

ok gkoehler@

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Support using the FPU and AltiVec registers in userland. The registers are
unconditionally saved upon context switch when they are in use.

Planting the first seed for OpenBSD/powerpc64.