[msuozzo]

Get git2 build running for the wasm32-wasip1 target. Given its lack of
socket support, this necessarily excludes the https and ssh features
for now (although wasip2 does add sockets).

The only change for non-WASI users is that libgit2-sys bumps the version
of libz-sys to 1.1.30 (see rust-lang/libz-sys#273).

On WASI, libgit2-sys requires the vendored feature, so libgit2 can be
compiled with a few local changes:

• NO_MMAP is defined.
• GIT_THREADS is off, ensuring wasm32-wasip1-threads won't build,
  which would otherwise make git2 Send types unsound.
• streams/socket.c is stubbed out to return an error.
• libgit2-sys/wasi/ stubs the user and process IDs and pwd.h, which
  wasi-libc lacks. The home directory comes from $HOME.
• -Wno-incompatible-pointer-types works around a type mismatch in
  integer.h until integer: use type-generic overflow intrinsics for size_t libgit2/libgit2#7406 lands.

git2 itself needed two fixes to work on WASI. Its path conversions only
had unix and windows versions, so a wasi-specific variant is needed to
compile. std's env::join_paths also always fails on WASI, which made
every Repository::open_ext and discover_path call fail. The fix is
to re-implement those joins for wasi ourselves.

The new WASI CI job builds with wasi-sdk and runs the tests under
wasmtime on stable, beta and nightly. On MSRV (1.87), CI only builds,
since std's remove_dir_all is buggy on WASI before Rust 1.94. git2
itself doesn't use it.

Most of the test diff swaps TempDir::new() for a test::tempdir()
helper. std has no temp directory on WASI, so the helper points tempfile
at /tmp, which the CI runner preopens.

Four tests are skipped on WASI:

• compile_fail runs cargo.
• non_utf8_branch needs non-UTF-8 paths.
• keeping_original_author_msg and prune remove directories through
  paths with a trailing slash, which wasmtime rejects pending release of
  the fix (wasi: remove directories named with a trailing slash bytecodealliance/wasmtime#14662).

[DanielEScherzer]

not going to pretend like I understand everything here, but some suggestions

View changes since this review

[msuozzo]

I intend to incorporate the changes from #1316, which run the test suite on WASI, once libz-sys releases the fix they need (rust-lang/libz-sys#276).

[msuozzo]

libz-sys 1.1.30 is out, so I've folded in #1316. libgit2-sys now requires 1.1.30, and the WASI job runs the test suite under wasmtime.

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.