Enable LLVM_ENABLE_RUNTIMES build of Flang-RT for flang-x86_64-windows (#383)

While #333 tried to update all buildbots all at once, this starts with
updating just one buildbot to test the `LLVM_ENABLE_RUNTIMES=flang-rt`
configuration.

The builder is currently running in staging here:
https://lab.llvm.org/staging/#/builders/36

Author: Meinersbur

buildbot/osuosl/master/config/builders.py

@@ -2524,7 +2524,7 @@
     'workernames' : ["minipc-ryzen-win"],
     'builddir': "flang-x86_64-windows",
     'factory' : UnifiedTreeBuilder.getCmakeWithNinjaBuildFactory(
-                    depends_on_projects=['llvm','mlir','clang','flang'],
+                    depends_on_projects=['llvm','mlir','clang','flang','flang-rt'],
                     checks=['check-flang'],
                     install_dir="flang.install",
                     extra_configure_args=[

zorg/buildbot/process/factory.py

@@ -7,6 +7,7 @@
 
 _all_runtimes = frozenset([
     "compiler-rt",
+    "flang-rt",
     "libc",
     "libcxx",
     "libcxxabi",