Compile error for static compiled Java module with `BuildInfo`

[lefou]

When the BuildInfo modules is used in a JavaModule, and buildInfoStaticCompiled = true, compilation fails:

[info] compiling 1 Java source to /home/lefou/work/opensource/mill/out/main/client/compile.dest/classes ...
[error] /home/lefou/work/opensource/mill/out/main/client/buildInfoSources.dest/mill/main/client/BuildInfo.java:8:1: cannot find symbol
[error]   symbol:   class Map
[error]   location: class mill.main.client.BuildInfo
[error] Map
[error] /home/lefou/work/opensource/mill/out/main/client/buildInfoSources.dest/mill/main/client/BuildInfo.java:8:1: cannot find symbol
[error]   symbol:   class HashMap
[error]   location: class mill.main.client.BuildInfo