Enable leak checker on Windows

[RalfJung]

Currently, the leak checker is disabled on Windows. This is because even a NOP program reports a leak:

The following memory was leaked:
alloc1821 (Rust heap, size: 40, align: 8) {
    0x00 │ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ │ ░░░░░░░░░░░░░░░░
    0x10 │ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ │ ░░░░░░░░░░░░░░░░
    0x20 │ __ __ __ __ __ __ __ __                         │ ░░░░░░░░
}
alloc1965 (Rust heap, size: 40, align: 8) {
    0x00 │ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ │ ░░░░░░░░░░░░░░░░
    0x10 │ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ │ ░░░░░░░░░░░░░░░░
    0x20 │ __ __ __ __ __ __ __ __                         │ ░░░░░░░░
}
alloc1997 (Rust heap, size: 24, align: 8) {
    0x00 │ ╾─────alloc1949+0─────╼ 00 00 00 00 00 00 00 00 │ ╾──────╼........
    0x10 │ 01 00 00 00 __ __ __ __                         │ ....░░░░
}
alloc2395 (Rust heap, size: 40, align: 8) {
    0x00 │ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ │ ░░░░░░░░░░░░░░░░
    0x10 │ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ │ ░░░░░░░░░░░░░░░░
    0x20 │ __ __ __ __ __ __ __ __                         │ ░░░░░░░░
}
alloc2445 (Rust heap, size: 40, align: 8) {
    0x00 │ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ │ ░░░░░░░░░░░░░░░░
    0x10 │ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ │ ░░░░░░░░░░░░░░░░
    0x20 │ __ __ __ __ __ __ __ __                         │ ░░░░░░░░
}
alloc1949 (fn: std::sys_common::thread_local::register_dtor_fallback::run_dtors)

This leak is caused by static sys:common::mutex::Mutex, which store a pointer to some Rust heap allocation, cast to an integer (so even with #940 resolved, we do not "see" the pointer).

Even on a Windows host, you can avoid this problem by cross-running your program with --target x86_64-unknown-linux-gnu.

[RalfJung]

rust-lang/rust#70765 should fix this.

[RalfJung]

See #1318 for the general issue with the leak checker and ptr-int casts (but just to get basic Windows support in the leak checker, a more targeted solution could suffice).

[RalfJung]

I thought implementing SRWLock would fix this, but there are unfortunately still some leaks left:

alloc10490 (Rust heap, size: 12, align: 4) {
    ╾a10426[<24213>] (4 ptr bytes)╼ 01 00 00 00 00 00 00 00             │ ╾──╼........
}
alloc11048 (Rust heap, size: 12, align: 4) {
    ╾a10989[<25532>] (4 ptr bytes)╼ 02 00 00 00 24 05 02 00             │ ╾──╼....$...
}

Both of these are allocated in std::sys::windows::thread_local::register_dtor, which manages a lock-free concurrent linked list of destructors, thus running into #1318.