Dependency windows-sys should be only on windows

[WhyNotHugo]

Dependency windows-sys should be gated via:

[target.'cfg(target_os = "windows")'.dependencies]

Currently it's included unconditionally, so builds fail on Linux:

error[E0425]: cannot find type `WSADATA` in this scope
    --> /builds/raspbeguy/aports/testing/lore/tmp/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/windows-sys-0.61.2/src/Windows/Win32/Networking/WinSock/mod.rs:167:99
     |
 167 | windows_link::link!("ws2_32.dll" "system" fn WSAStartup(wversionrequested : u16, lpwsadata : *mut WSADATA) -> i32);
     |                                                                                                   ^^^^^^^
...
5732 | pub struct WSPDATA {
     | ------------------ similarly named struct `WSPDATA` defined here
     |
help: a struct with a similar name exists
     |
 167 - windows_link::link!("ws2_32.dll" "system" fn WSAStartup(wversionrequested : u16, lpwsadata : *mut WSADATA) -> i32);
 167 + windows_link::link!("ws2_32.dll" "system" fn WSAStartup(wversionrequested : u16, lpwsadata : *mut WSPDATA) -> i32);
     |
error[E0425]: cannot find type `SERVENT` in this scope
   --> /builds/raspbeguy/aports/testing/lore/tmp/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/windows-sys-0.61.2/src/Windows/Win32/Networking/WinSock/mod.rs:237:135
    |
237 | ...CSTR, proto : windows_sys::core::PCSTR) -> *mut SERVENT);
    |                                                    ^^^^^^^ not found in this scope
error[E0425]: cannot find type `SERVENT` in this scope
   --> /builds/raspbeguy/aports/testing/lore/tmp/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/windows-sys-0.61.2/src/Windows/Win32/Networking/WinSock/mod.rs:238:114
    |
238 | windows_link::link!("ws2_32.dll" "system" fn getservbyport(port : i32, proto : windows_sys::core::PCSTR) -> *mut SERVENT);
    |                                                                                                                  ^^^^^^^ not found in this scope
error[E0425]: cannot find type `XSAVE_FORMAT` in this scope
    --> /builds/raspbeguy/aports/testing/lore/tmp/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/windows-sys-0.61.2/src/Windows/Win32/System/Diagnostics/Debug/mod.rs:6372:22
     |
6372 |     pub LegacyState: XSAVE_FORMAT,
     |                      ^^^^^^^^^^^^ not found in this scope
error[E0425]: cannot find type `XSAVE_FORMAT` in this scope
    --> /builds/raspbeguy/aports/testing/lore/tmp/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/windows-sys-0.61.2/src/Windows/Win32/System/Diagnostics/Debug/mod.rs:6372:22
     |
6372 |     pub LegacyState: XSAVE_FORMAT,
     |                      ^^^^^^^^^^^^ not found in this scope
     |
help: you might be missing a type parameter
     |
6371 | pub struct XSAVE_AREA<XSAVE_FORMAT> {
     |                      ++++++++++++++

For some reason, they don't fail on x86_64, but fail on at least 5 other architectures.

[subhramit]

Have filed #45 for this.

cc @mjansson, @ragnarula
/ @matt-hoffman-epic, @peter-lockhart-pub