Compile on amd64 Haiku (#4473)
* Compile on amd64 Haiku
Use sigcontext (somewhat like win32, or x86) on Haiku amd64.
On amd64, Haiku doesn't have issues with marshalling 64-bit values,
but it currently does have issues with SGen either causing a stall
or a core dump. As such, while it can compile the stdlib (further
than x86 got), it's still a work in progress.
* Use set_real_time_clock for sys-time.c on Haiku
* Get mono-boehm compiling on Haiku again
It still doesn't work. Initialization will call GC_mark_from, which
will cause a segmentation fault as it decrements pointers. (Mono
will enter an infinite loop in mono_get_hazardous_pointer as a result.)
For now, mono-sgen will continue to be used by default.