If I edit any source in src/jdk.internal.vm.compiler and then re-run make, I get this error:

dsimon@kruger-5 ~/jdk-jdk> make CONF=macosx-x86_64-normal-server-release images
Building target 'images' in configuration '/Users/dsimon/jdk-jdk/build/macosx-x86_64-normal-server-release'
Compiling 44 files for jdk.httpserver
Updating support/modules_libs/java.base/server/libjvm.dylib due to 12 file(s)
Exception in thread "main" java.lang.Error: /Users/dsimon/jdk-jdk/build/macosx-x86_64-normal-server-release/support/gensrc/jdk.internal.vm.compiler/module-info.java.extra, line 185, multiple provides jdk.vm.ci.services.JVMCIServiceLocator "provides jdk.vm.ci.services.JVMCIServiceLocator with"
at build.tools.module.GenModuleInfoSource$Parser.newError(GenModuleInfoSource.java:762)
at build.tools.module.GenModuleInfoSource$ModuleInfo.process(GenModuleInfoSource.java:436)
at build.tools.module.GenModuleInfoSource$ModuleInfo.parseExtra(GenModuleInfoSource.java:380)
at build.tools.module.GenModuleInfoSource$ModuleInfo.access$100(GenModuleInfoSource.java:175)
at build.tools.module.GenModuleInfoSource.<init>(GenModuleInfoSource.java:136)
at build.tools.module.GenModuleInfoSource.main(GenModuleInfoSource.java:112)

The only solution is to remove /Users/dsimon/jdk-jdk/build/macosx-x86_64-normal-server-release/support/gensrc/jdk.internal.vm.compiler/module-info.java.extra and then re-run make.

This can be reproduced in a clean open repo as follows:
> make
> touch src/jdk.internal.vm.compiler/share/classes//org.graalvm.compiler.hotspot/src/org/graalvm/compiler/hotspot/HotSpotGraalJVMCIServiceLocator.java
> make

This problem occurs when building in both the open and closed repos.