[zorg] Update flang out-of-tree builder

[rovka]

Summary

...to use the build directory instead of the install
directory for clang. This matches recent changes
to the documentation:
https://reviews.llvm.org/D117100

[awarzynski]

Makes sense, thanks for the update!

zorg/buildbot/builders/FlangBuilder.py

def getFlangOutOfTreeBuildFactory(
 
     if env is None:
         env = dict()
 
     f = getCmakeWithNinjaBuildFactory(
             depends_on_projects=['llvm','clang','mlir'],
             obj_dir="build_llvm",
             checks=[],
-            install_dir="install",
             clean=clean,
             extra_configure_args=llvm_extra_configure_args,
             env=env,
             **kwargs)
 
     if checks is None:
         checks = ['check-all']
 
CmakeCommand.applyRequiredOptions(flang_cmake_args, [
         ])
 
     flang_obj_dir = "build_flang"
     flang_src_dir = "{}/flang".format(f.monorepo_dir)
 
     # Add LLVM_DIR and MLIR_DIR to the CMake invocation.
     llvm_dir = "{}/lib/cmake/llvm".format(f.obj_dir)
     mlir_dir = "{}/lib/cmake/mlir".format(f.obj_dir)
-    clang_dir = "{}/lib/cmake/clang".format(f.install_dir)
+    clang_dir = "{}/lib/cmake/clang".format(f.obj_dir)
     CmakeCommand.applyRequiredOptions(flang_cmake_args, [
         # We actually need the paths to be relative to the source directory,
         # otherwise find_package can't locate the config files.
         ('-DLLVM_DIR:PATH=',
             LLVMBuildFactory.pathRelativeTo(llvm_dir, flang_src_dir)),
         ('-DMLIR_DIR:PATH=',
             LLVMBuildFactory.pathRelativeTo(mlir_dir, flang_src_dir)),
         ('-DCLANG_DIR:PATH=',