Rename syscalls.h/.cc to kernel_metadata.h/.cc
Move *name functions from util to kernel_metadata.
Rename signalname to signal_name
Clean up util.h
Remove unused #includes.
Add kernel_sigaction to kernel_abi.h
Add NativeArch typedef.
Make Sighandler architecture-independent.
Move syscalls autogenerated code to use Arch::kernel_sigaction.
Add test for rt_sigaction's out-parameter.
Switch some generated syscalls code to use kernel_abi structures.