MSVC can't explicitly cast a struct to a typedef of itself (ie. f128 to i128). Added a
set of macros to handle float casting, and to not produce a cast for this specific
case on MSVC. A better approach would probably be to know if the cast is redundant
and not do it.
- Forward declare int builtins, so the definitions aren't assumed incorrectly
- Add define to handle MSVC not support static const in function parameter array lengths
- Fixup several spots where int128 support was assumed.
- Support zig_align
- Support zig_export
- Stub out some missing non-builtin functions
- Added StringLiteral to automatically split string literals when they get to 16380 in size,
which is the maxmimum pre-concatenation string literal size on MSVC.
In general the C backend should lower to human-maintainable C code
whenever possible. Directly using C types that one would use when
writing C code is one part of the strategy.
The concern with including stdint.h is C89 compatibility. Well, we can
just check the C std lib version before deciding to include that header.
