std: Add Win64 types to libc
std: Fix write() ffi on Win64
std: Add Win64 ffi binding

Some extern blobs are duplicated without "stdcall" abi,
since Win64 does not use any calling convention.
(Giving "stdcall" abi causes llvm producing wrong bytecode.)
Set Win64 target_triple same as mingw-w64
rt: Make valgrind Win64-compatible
rt: Support SEH/SJLJ personality routine