Complete depends_on_projects for the bot flang-runtime-cuda-gcc (#923)

Note the parameter `enable_runtimes="auto"` by default in
UnifiedTreeBuilder.getCmakeExBuildFactory(). So `enable_runtimes` will
be constructed automatically from the list `depends_on_projects`:
```
self.enable_runtimes = self.depends_on_projects.intersection(_all_runtimes)
```
where `_all_runtimes = ["compiler-rt", "flang-rt", "libc", "libcxx",
"libcxxabi", "libunwind", "openmp"]`