[manifest] Fix warnings in 5.3 toolchains

[lorentey]

Requiring a 5.3 toolchain introduced a number of new warnings, because of the new resource files feature. Explicitly exclude CMake files and .gyb files from package targets.

Checklist

• I've read the Contribution Guidelines
• My contributions are licensed under the Swift license.
• I've followed the coding style of the rest of the project.
• I've added tests covering all new code paths my change adds to the project (if appropriate).
• I've verified that my change does not break any existing tests.
• I've updated the documentation if necessary.

[lorentey]

@swift-ci test

[lorentey]

@swift-ci test Linux platform