Adds target info for the PSX. Builds fine with the following:
```zig
const target = b.resolveTargetQuery(.{
.os_tag = .psx,
.cpu_arch = .mipsel,
});
```
the only "problem" being that it spits out an error from LLVM even
though generating an object file succeeds:
```sh
❯ zig build
install
└─ install generated to main.o
└─ compile obj obj Debug mipsel-psx failure
error: warning: MIPS-I support is experimental
```
The compiler actually doesn't need any functional changes for this: Sema
does reification based on the tag indices of `std.builtin.Type` already!
So, no zig1.wasm update is necessary.
This change is necessary to disallow name clashes between fields and
decls on a type, which is a prerequisite of #9938.
Alex Rønne Petersen