How to properly upgrade Gradle in composite builds?

[ams_tschoening (Thorsten Schöning)]

This is related to the following question:

Composite builds and different versions of Gradle wrapper

I have a composite build consisting of multiple projects A+B+C, while A provides some plugins to B and C and is therefore included. It’s pretty much used as a replacement for buildSrc in B and C. A needs to use Gradle 5.0 RC1 for some reasons, while B and C do fine with 4.10. When executing gradlew build in A 5.10 is used as expected because of gradle-wrapper.properties. The problem is that when executing the same in B or C the build fails with compilation errors, because Gradle 4.10 is used an…