Created by: egrimley
Struct sigcontext and friends may or may not be defined by C library header files. To have these types defined reliably, without redefinition errors, we add the "kernel" prefix. Also:
- add AArch64 struct kernel_sigcontext
- #include "include/sigcontext.h" in os_public.h
- remove _BITS* and _ASM* #defines in sigcontext.h
- replace some TABs with spaces
- split some long lines