[gobject-introspection] Fix x86-windows build

[mkhon]

Describe the pull request

Fix x86-windows build (accidentally disabled when fixing build failures for the initial port PR)

• What does your PR fix?

• Which triplets are supported/not supported? Have you updated the CI baseline?

all

• Does your PR follow the maintainer guide?

Yes

• If you have added/updated a port: Have you run ./vcpkg x-add-version --all and committed the result?

Yes

If you are still working on the PR, open it as a Draft: https://github.blog/2019-02-14-introducing-draft-pull-requests/

[github-actions]

You have modified or added at least one vcpkg.json where a "license" field is missing.
If you feel able to do so, please consider adding a "license" field to the following files:

• ports/gobject-introspection/vcpkg.json

Valid values for the license field are listed at https://spdx.org/licenses/

[ras0219-msft]

This LGTM, though the supports line continues to be extremely strange w.r.t. the actual code in the port.

[mkhon]

@ras0219-msft cross-building requires more work as gobject-introspection builds introspection data for itself.

When introspection data is being built, gobject-introspection uses host tools (host python) to run code generation, then compiles the executable (again, using python tooling) and executes it to dump introspection data.

This executable should be built for host (as it runs on host during the build), however the build environment at this point is configured by vcpkg to build for target.

Most likely gobject (host) introspection tools should reset the build environment to always build for host as these binaries are never executed on target. This requires more work. I will work on that in a separate PR.