Update to clang-sys 1.0.0

[KyleMayes]

First, an update:

Due to issues where incompatible versions of clang-sys pulled in by different versions of bindgen would be rejected by Cargo due to duplicate package.links Cargo manifest keys, I have today published the following patch releases for previous minor versions of clang-sys so that they can co-exist peacefully (for more info, see this issue):

• v0.29.4
• v0.28.2
• v0.27.1

However, this was accomplished with a hack, essentially republishing clang-sys under a different name (clang-sys-linkage) as v1.0.0 and then re-exporting that crate from the above patch versions.

EDIT: Unfortunately the above strategy did not work due to API incompatibilities I was not aware of.

Going forward, clang-sys has been published as v1.0.0 so that future additions to the API can be added in a backwards-compatible way (since 1.0.0 and 1.1.0 are compatible but v0.29.0 and v0.30.0 are not) so that users will eventually not ever have multiple versions of clang-sys in their dependency tree.

The bump to v1.0.0 also includes these changes:

• warnings from the clang-sys build script about llvm-config failing to execute are no longer printed unless the build script fails to find an instance of libclang
• update libloading version to 0.6.0 since 0.5.0 was causing some people problems
• Clang 10 support (which is almost entirely new OpenMP enum values, not very exciting)

[kulp]

It looks as if libloading 0.6.0 requires at least Rust 1.40.0 due to non-exhaustive enums. That seems like a big jump for MSRV from our current 1.34.0, although @emilio has also said we could update the MSRV of bindgen.

[emilio]

Yeah, let's update the MSRV here if you want, let me know if you need help with it.

This looks great otherwise, thanks for your work in clang-sys @KyleMayes!

[KyleMayes]

Updated MSRV to 1.40.0 and the tests are passing now.

[emilio]

Thank you!