Fix Windows compiler invocation to not create new console windows

[luser]

235239a changed how we spawn the sccache server process on Windows to make it detached, but in the process it made it so that when the server spawns a compiler process it creates a new console window. This is noticeable if you run cargo test test_sccache_command on Windows, you'll see several console windows pop up.

[luser]

The original Python code was spawning the process with the DETACHED_PROCESS flag:

sccache/sccache.py

Line 60 in e3f5fb2

creationflags=8, # DETACHED_PROCESS

the Rust code is also passing CREATE_NEW_PROCESS_GROUP:

sccache/src/commands.rs

Line 145 in 5591191

CREATE_UNICODE_ENVIRONMENT | DETACHED_PROCESS | CREATE_NEW_PROCESS_GROUP,

I'll try removing that and see if it makes a difference. If not it might be some other difference in the Rust process spawning code vs. Python's subprocess.

[luser]

...that's not it.

[luser]

...that's not it.

[luser]

Oh, hah! This bug existed in the Python implementation as well, and @glandium fixed it in this commit by passing CREATE_NO_WINDOW in the CreateProcess flags:
glandium@b259421

[RReverser]

@luser @alexcrichton I recently started using sccache, and am seeing a very similar issue (new console windows occasionally flickering with sccache). I know this one was fixed a long time ago, but I wonder if it was reintroduced again?

[Systemcluster]

Using sccache 0.2.9, tested on Windows 10 with PowerShell and CMD, this is (still or again) occurring currently. @luser would you mind re-opening this issue?

[luser]

Can you open a new issue on this? I think that'd be less confusing.