Rollup merge of #150905 - PaulDance:patches/unsupport-win7-hostname, r=Mark-Simulacrum

Fix(lib/win/net): Remove hostname support under Win7

Fixes rust-lang/rust#150896. `GetHostNameW` is not available under Windows 7, leading to dynamic linking failures upon program executions. For now, as it is still unstable, this therefore appropriately cfg-gates the feature in order to mark the Win7 as unsupported with regards to this particular feature. Porting the functionality for Windows 7 would require changing the underlying system call and so more work for the immediate need.

@rustbot label C-bug O-windows-7 T-libs A-io

Author: matthiaskrgr