Little-endian format

The format includes endianness variations that complicate toolchain support. I think we should use a little-endian format universally, regardless of the target system's native endianness. On the big-endian z/Architecture, this is efficient; the LOAD REVERSED instructions used by the bswap versions in the following program don't even require extra instructions.

#define WIDTH(x) \
typedef __UINT##x##_TYPE__ [[gnu::aligned(1)]] uint##x; \
uint##x load_inc##x(uint##x *p) { return *p+1; } \
uint##x load_bswap_inc##x(uint##x *p) { return __builtin_bswap##x(*p)+1; }; \
uint##x load_eq##x(uint##x *p) { return *p==3; } \
uint##x load_bswap_eq##x(uint##x *p) { return __builtin_bswap##x(*p)==3; }; \

WIDTH(16);
WIDTH(32);
WIDTH(64);

My blog post had a TODO chapter about CTF Frame. I spent some time today to read the spec and add my analysis here: https://maskray.me/blog/2020-11-08-stack-unwinding#sframe