This ports some signal setup and handling bits to Rust.
The signal handling machinery requires walking over the list of known signals;
that's not supported by the Signal type. Rather than duplicate the list of
signals yet again, switch back to a table, as we had in C++.
This also adds two further pieces which were neglected by the Signal struct:
1. Localize signal descriptions
2. Support for integers as the signal name
The conversion to usize is used for array accesses, so negative values
would cause crashes either way. Let's do it earlier so we can get rid of
the suspect C-style cast.
Signal is a newtype around NonZeroI32. We could use NonZeroU8 since all signal
values comfortably fit, but using i32 lets us avoid a fallible attempt at
narrowing values returned from the system as integers to the narrower u8 type.
Known signals are explicitly defined as constants and can be matched against
with equality or with pattern matching in a `match` block. Unknown signal values
are passed-through without causing any issues.
We're using per-OS targeting to enable certain libc SIGXXX values - we could
change this to dynamically detecting what's available in build.rs but then it
might not match what libc exposes, still giving us build failures.
wchar.rs should not import let alone reexport FFI strings.
Stop re-exporting utf32str! because we use L! instead.
In wchar_ffi.rs, stop re-exporting cxx::CxxWString because that hasn't
seen adoption.
I think we should use re-exports only for aliases like "wstr" or for aliases
into internal modules.
So I'd probably remove `pub use wchar_ffi::wcharz_t = crate::ffi::wcharz_t`
as well.
More ugliness with types that cxx bridge can't recognize as being POD. Using
pointers to get/set `termios` values with an assert to make sure we're using
identical definitions on both sides (in cpp from the system headers and in rust
from the libc crate as exported).
I don't know why cxx bridge doesn't allow `SharedPtr<OpaqueRustType>` but we can
work around it in C++ by converting a `Box<T>` to a `shared_ptr<T>` then convert
it back when it needs to be destructed. I can't find a clean way of doing it
from the cxx bridge wrapper so for now it needs to be done manually in the C++
code.
Types/values that are drop-in ready over ffi are renamed to match the old cpp
names but for types that now differ due to ffi difficulties I've left the `_ffi`
in the function names to indicate that this isn't the "correct" way of using the
types/methods.
