* CLI: `-target [name]` instead of `--target-*` args.
This matches clang's API.
* `builtin.Environ` renamed to `builtin.Abi`
- likewise `builtin.environ` renamed to `builtin.abi`
* stop hiding the concept of sub-arch. closes#1526
* `zig targets` only shows available targets. closes#438
* include all targets in readme, even those that don't
print with `zig targets` but note they are Tier 4
* refactor target.cpp and make the naming conventions
more consistent
* introduce the concept of a "default C ABI" for a given
OS/Arch combo. As a rule of thumb, if the system compiler
is clang or gcc then the default C ABI is the gnu ABI.
It's needed because LLVM emits library calls to compiler-rt when hardware lacks
functionality, for example, 64-bit integer multiplication on 32-bit x86.
This library is automatically built as-needed for the compilation target and
then statically linked and therefore is a transparent dependency for the
programmer.
Any bugs should be solved by trying to duplicate the bug upstream.
If the bug exists upstream, get it fixed with the LLVM team and then port
the fix downstream to Zig.
If the bug only exists in Zig, something went wrong porting the code,
and you can run the C code and Zig code side by side in a debugger
to figure out what's happening differently.