Fix windows cache permission

[chenyukang]

Description

Fix issue #2454 , default WASMER_CACHE_DIR is not right for Windows.
Add more detailed messages for creating cache directory failure.

close #2454.

[Hywan]

Thank you for the PR! One last question before approving the PR.

[syrusakbary]

If not provided, WASMER_CACHE_DIR will be WASMER_DIR + "/cache"

In this case, I think we should go to the value that worked before:

Suggested change

	Root: HKCU; Subkey: "Environment"; ValueType:string; ValueName: "WASMER_CACHE_DIR"; \
	ValueData: "{app}\cache"; Flags: preservestringtype
	Root: HKCU; Subkey: "Environment"; ValueType:string; ValueName: "WASMER_CACHE_DIR"; \
	ValueData: "{%USERPROFILE}\.wasmer\cache"; Flags: preservestringtype

[chenyukang]

I think it's better not to set a register default value for it on Windows. We can keep the consistent usage style with Unix/Linux OS.

If users want to specify a cache directory, they can set an environment variable WASMER_CACHE_DIR, otherwise, env::temp_dir() will be used and it's safe for caching files.

/// Get the cache dir
pub fn get_cache_dir() -> PathBuf {
    match env::var("WASMER_CACHE_DIR") {
        Ok(dir) => {
            let mut path = PathBuf::from(dir);
            path.push(VERSION);
            path
        }
        Err(_) => {
            // We use a temporal directory for saving cache files
            let mut temp_dir = env::temp_dir();
            temp_dir.push("wasmer");
            temp_dir.push(VERSION);
            temp_dir
        }
    }
}

What do you think? @syrusakbary

[syrusakbary]

Looks great, merging!

[syrusakbary]

bors r+

[bors]

Build succeeded:

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• Test cross-compile on linux
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• Test on linux-x64
• Test on macos-x64
• Test on windows-x64