Support gcc-less installation on Windows

[vadimcn]

• Support gcc-less installation on Windows. To do so in unattended mode run:<intaller>.exe /TYPE=compact /SILENT.
• Do not require admin privileges to install.

cc #19519

[alexcrichton]

r? @brson

@vadimcn, do you have a copy of the installer that I'd be able to test out locally as well?

[vadimcn]

@alexcrichton: here you go: https://drive.google.com/file/d/0ByXV1AdBUyEONlRTd2VxbXBRUjA/view?usp=sharing

[brson]

Thanks @vadimcn

[alexcrichton]

@vadimcn I ran this installer locally and noticed a few things:

• I could never uncheck "Rust compiler and standard libraries", just checking this is intentional, right?
• I got an error: "CreateFile failed; code 5. Access is denied". Is this because I'm not installing with administrator privileges, but my previous installation was installed with admin privileges?
• Upon deleting my existing C:\Program Files (x86)\Rust folder, I got the error "Setup was unable to create the directory ..." and I was unable to install.
• I was initially prompted with a prompt to elevate privileges, but I couldn't reproduce this, it may have been related to my previous installation existing.

[vadimcn]

Uh-huh, I never install Rust into "Program Files", so I didn't notice that problem. I guess I am gonna have to revert the "Do not require admin privileges to install" bit. Which is a pity, because that precludes non-admins from installing it.

[alexcrichton]

I'd actually love to keep the ability to not require admin privileges! Is there a way to default to a different folder which doesn't require admin privileges?

[vadimcn]

re-r+ ?

[alexcrichton]

@vadimcn hm I thought I included this in the rollup? Does the new commit mean that each installation of rust is placed in a new directory?

[vadimcn]

hm I thought I included this in the rollup?

Was it? Hmm, this PR is still open. Should I open a new one?

Does the new commit mean that each installation of rust is placed in a new directory?

Not every time, but it'll include version number and release channel, like so: C:\Rust-0.13.0-dev. Do you want something more stable?

[alexcrichton]

Rollup PRs only actually get closed if the HEAD is the same when its merged as when I merged it locally, so you may have pushed after I made the rollup (that's ok). It does mean that at least some portions of this PR are currently in master.

I only worry because it's different than all our other platforms. I personally only want to overwrite the previous installation, but I know that people may differ! Perhaps an option could be provided?