Simplified Target-Specific Dependencies

[randomPoison]

As I understand it to specify target-specific dependencies you need to use the full target triple:

[target.x86_64-unknown-linux-gnu.dependencies]
openssl = "1.0.1"

[target.x86_64-pc-windows-gnu.dependencies]
winhttp = "0.4.0"

But a platform like Windows has multiple target triples and if I want to declare windows specific dependencies I have to repeat them across all of the target triples:

[target.i686-pc-windows-gnu.dependencies]
libc = "*"
winapi = "*"
ole32-sys = "*"

[target.x86_64-pc-windows-gnu.dependencies]
libc = "*"
winapi = "*"
ole32-sys = "*"

[target.x86_64-pc-windows-msvc.dependencies]
libc = "*"
winapi = "*"
ole32-sys = "*"

This quickly becomes tedious. I'd like a simplified version where I can specify a set of dependencies for a platform, something like [target.windows.dependencies]. The broader platform sets could match those used by the [cfg()] attribute (e.g. "windows", "unix", "macos", etc.).

Related to #1197 this could also be applied to features as [target.windows.features].

Thanks.

[alexcrichton]

Dupe of #1007, but thanks for the report!

[randomPoison]

Sorry about that! Must have missed it when looking over the existing issues.