Switch to pkg-config-rs from GIT for working around MSVC linking issues

[sdroege]

This PR removes a workaround from the appveyour setup which should be unneeded with latest pkg-config-rs. Previously for msvc builds the library paths were not taken into account properly.

Once this also works on the servo appveyour, a new pkg-config-rs release will be made and the patch section can be removed again from Cargo.toml. I'll update the PR then.

---

• ./mach build -d does not report any errors
• ./mach test-tidy does not report any errors
• These changes fix #21158 (comment)

• There are tests for these changes OR
• These changes do not require tests because they are changes to the CI setup

---

This change is 

cc @ferjm

[highfive]

Thanks for the pull request, and welcome! The Servo team is excited to review your changes, and you should hear from @paulrouget (or someone else) soon.

[highfive]

Heads up! This PR modifies the following files:

• @edunham: appveyor.yml

[sdroege]

   = note: LINK : fatal error LNK1181: cannot open input file 'z.lib.lib'

First of all it seems like zlib was taken from the GStreamer binaries (instead of whatever was there before) since the webaudio PR. Second it looks like this still uses the old pkg-config for some reason.

I'll check this later.

[bors-servo]

☔ The latest upstream changes (presumably #21490) made this pull request unmergeable. Please resolve the merge conflicts.

[sdroege]

Closing in favour of #21515, which is literally the same change :)