[flang][CMake] Add missing dependency to generate Fortran module files (#91517)

Fixes bug #90769. Many thanks
to @Meinersbur for providing the initial thought and solution to this.

Author: mjklemm

llvm/runtimes/CMakeLists.txt

@@ -431,8 +431,10 @@ if(runtimes)
       set(LIBOMP_MODULES_INSTALL_PATH "${CMAKE_INSTALL_INCLUDEDIR}/flang")
       # TODO: This is a workaround until flang becomes a first-class project
       # in llvm/CMakeList.txt.  Until then, this line ensures that flang-new is
-      # built before "openmp" is built as a runtime project.
-      list(APPEND extra_deps "flang-new")
+      # built before "openmp" is built as a runtime project.  Besides "flang-new"
+      # to build the compiler, we also need to add "module_files" to make sure
+      # that all .mod files are also properly build.
+      list(APPEND extra_deps "flang-new" "module_files")
     endif()
     foreach(dep opt llvm-link llvm-extract clang clang-offload-packager)
       if(TARGET ${dep})