* Implement fd_filestat_get for all platforms

* Remove an old comment

* Remove panics from the syscall wrappers

* Return WASI error type

* Reuse Metadata if possible to save syscalls.

* Refactor the change for two separate fd_filestat_get_impl

* Refactor error handling

* Initial implementation

* Not use grow as it is makes debug builds very slow

* Use Pages::BYTE_SIZE for LINEAR_MEMORY_PAGE_SIZE

* Tidy docs.

* Use memory_units from git.

The global map for storing `*Func` objects previously stored `*Store`,
but that creates a reference cycle between the Rust and the Go heaps
which can't be cleaned up. Instead this commit updates the logic to
instead use a "thread local" variable to temporarily store the current
freelist during a call and moves the storage outside of the global
variables. This should allow everything to get garbage collected as
usual.

Closes bytecodealliance#42

This gets us another step closer to running the Wasmtime tests.

…ecodealliance#42)

This patch improves upon bytecodealliance#42. In addition it renames the flag, so to build a compiler & runtime without linearity checking one has to supply the following:

```shell
$ cargo build --features=default,unsafe_disable_continuation_linearity_check
```

This patch improves upon bytecodealliance#42. In addition it renames the flag, so to build a compiler & runtime without linearity checking one has to supply the following:

```shell
$ cargo build --features=default,unsafe_disable_continuation_linearity_check
```

bytecodealliance#47)

* Improve compile option for disabling the continuation linearity check.

This patch improves upon bytecodealliance#42. In addition it renames the flag, so to build a compiler & runtime without linearity checking one has to supply the following:

```shell
$ cargo build --features=default,unsafe_disable_continuation_linearity_check
```

…odealliance#42)

This patch is a follow up on PR bytecodealliance#35. It partially addresses issue
presence of stack switching as older frame pointers are not guaranteed
to be greater than the current frame pointer (e.g. tracing across
stack boundaries).

Allow to map host directory as arbitary guest path

If we emit a value label alias for an instruction that isn't lowered,
then that signals that the value has been optimised out. However, since
it is an alias we know that the value also exists in an earlier vreg, so
we should skip the alias and use that instead.

This situation occurs often for memory indexes on AArch64. We translate
memory stores into instructions such as:

    v8 = iconst.i32 42
    v9 = uextend.i64 v6
    v10 = load.i64 notrap aligned readonly can_move checked v0+56
    v11 = iadd v10, v9
    v12 = iconst.i64 20
    v13 = iadd v11, v12  ; v12 = 20
    store little heap v8, v13  ; v8 = 42

Here, v6 is a memory index (which has a label) and v9 is an alias of the
memory index added by cast_index_to_pointer_ty(). This is lowered to:

     40c:       52800540        mov     w0, #0x2a                       // bytecodealliance#42
     410:       f9401c41        ldr     x1, [x2, bytecodealliance#56]
     414:       91005021        add     x1, x1, #0x14
     418:       b8384820        str     w0, [x1, w24, uxtw]

The uextend has been folded into the str, so v9 has been optimized
out. But v6 is still present in w24, so the debuginfo should use that
instead.

This fixes the following tests for AArch64:

    native_debug::lldb::dwarf_cold_block
    native_debug::lldb::dwarf_fib_wasm
    native_debug::lldb::dwarf_fib_wasm_dwarf5
    native_debug::lldb::dwarf_fib_wasm_split4
    native_debug::lldb::dwarf_fission
    native_debug::lldb::dwarf_fraction_norm
    native_debug::lldb::dwarf_imported_memory
    native_debug::lldb::dwarf_shared_memory
    native_debug::lldb::dwarf_simple
    native_debug::lldb::dwarf_spilled_frame_base

If we emit a value label alias for an instruction that isn't lowered,
then that signals that the value has been optimised out. However, since
it is an alias we know that the value also exists in an earlier vreg, so
we should skip the alias and use that instead.

This situation occurs often for memory indexes on AArch64. We translate
memory stores into instructions such as:

    v8 = iconst.i32 42
    v9 = uextend.i64 v6
    v10 = load.i64 notrap aligned readonly can_move checked v0+56
    v11 = iadd v10, v9
    v12 = iconst.i64 20
    v13 = iadd v11, v12  ; v12 = 20
    store little heap v8, v13  ; v8 = 42

Here, v6 is a memory index (which has a label) and v9 is an
extension of the memory index (which has a label alias, added by
cast_index_to_pointer_ty()). This is lowered to:

     40c:       52800540        mov     w0, #0x2a                       // bytecodealliance#42
     410:       f9401c41        ldr     x1, [x2, bytecodealliance#56]
     414:       91005021        add     x1, x1, #0x14
     418:       b8384820        str     w0, [x1, w24, uxtw]

The uextend has been folded into the str, so v9 has been optimised
out. But v6 is still present in w24, so the debuginfo should use that
instead.

This fixes the following tests for AArch64:

    native_debug::lldb::dwarf_cold_block
    native_debug::lldb::dwarf_fib_wasm
    native_debug::lldb::dwarf_fib_wasm_dwarf5
    native_debug::lldb::dwarf_fib_wasm_split4
    native_debug::lldb::dwarf_fission
    native_debug::lldb::dwarf_fraction_norm
    native_debug::lldb::dwarf_imported_memory
    native_debug::lldb::dwarf_shared_memory
    native_debug::lldb::dwarf_simple
    native_debug::lldb::dwarf_spilled_frame_base

If we emit a value label alias for an instruction that isn't lowered,
then that signals that the value has been optimised out. However, since
it is an alias we know that the value also exists in an earlier vreg, so
we should skip the alias and use that instead.

This situation occurs often for memory indexes on AArch64. We translate
memory stores into instructions such as:

    v8 = iconst.i32 42
    v9 = uextend.i64 v6
    v10 = load.i64 notrap aligned readonly can_move checked v0+56
    v11 = iadd v10, v9
    v12 = iconst.i64 20
    v13 = iadd v11, v12  ; v12 = 20
    store little heap v8, v13  ; v8 = 42

Here, v6 is a memory index (which has a label) and v9 is an
extension of the memory index (which has a label alias, added by
cast_index_to_pointer_ty()). This is lowered to:

     40c:       52800540        mov     w0, #0x2a                       // #42
     410:       f9401c41        ldr     x1, [x2, #56]
     414:       91005021        add     x1, x1, #0x14
     418:       b8384820        str     w0, [x1, w24, uxtw]

The uextend has been folded into the str, so v9 has been optimised
out. But v6 is still present in w24, so the debuginfo should use that
instead.

This fixes the following tests for AArch64:

    native_debug::lldb::dwarf_cold_block
    native_debug::lldb::dwarf_fib_wasm
    native_debug::lldb::dwarf_fib_wasm_dwarf5
    native_debug::lldb::dwarf_fib_wasm_split4
    native_debug::lldb::dwarf_fission
    native_debug::lldb::dwarf_fraction_norm
    native_debug::lldb::dwarf_imported_memory
    native_debug::lldb::dwarf_shared_memory
    native_debug::lldb::dwarf_simple
    native_debug::lldb::dwarf_spilled_frame_base