The big endian RISC-V effort is mostly driven by MIPS (the company) which is
pivoting to RISC-V, and presumably needs a big endian variant to fill the niche
that big endian MIPS (the ISA) did.
GCC already supports these targets, but LLVM support will only appear in 22;
this commit just adds the necessary target knowledge and checks on our end.
This mainly just moves stuff around.
Justifications for other changes:
* `KEVENT.FLAGS` is backed by `c_uint` because that's what the `kevent64` flags param takes (according to the 'latest' manpage from 2008)
* `MACH_RCV_NOTIFY` is a legacy name and `MACH_RCV_OVERWRITE` is deprecated (xnu/osfmk/mach/message.h), so I removed them. They were 0 anyway and thus couldn't be represented
as a packed struct field.
* `MACH.RCV` and `MACH.SEND` are technically the same 'type' because they can both be supplied at the same time to `mach_msg`. I decided to still keep them separate because
naming works out better that way and all flags except for `MACH_MSG_STRICT_REPLY` aren't shared anyway. Both are part of a packed union `mach_msg_option_t` which supplies a
helper function to combine the two types.
* `PT` is backed by `c_int` because that's what `ptrace` takes as a request arg (according to the latest manpage from 2015)
It doesn't really make sense for `target_util.canBuildLibCompilerRt`
(and its ubsan-rt friend) to take in `use_llvm`, because the caller
doesn't control that: they're just going to queue a sub-compilation for
the runtime. The only exception to that is the ZCU strategy, where we
effectively embed `_ = @import("compiler_rt")` into the Zig compilation:
there, the question does matter. Rather than trying to do multiple weird
calls to model this, just have `canBuildLibCompilerRt` return not just a
boolean, but also differentiate the self-hosted backend being capable of
building the library vs only LLVM being capable. Logic in `Compilation`
uses that difference to decide whether to use the ZCU strategy, and also
to disable the library if the compiler does not support LLVM and it is
required.
Also, remove a redundant check later on, when actually queuing jobs.
We've already checked that we can build `compiler_rt`, and
`compiler_rt_strat` is set accordingly. I'm guessing this was there to
work around a bug I saw in the old strategy assignment, where support
was ignored in some cases.
Resolves: #24623
