Index: llvm/CMakeLists.txt
===================================================================
--- llvm/CMakeLists.txt
+++ llvm/CMakeLists.txt
@@ -64,8 +64,12 @@
 # This allows an easy way of setting up a build directory for llvm and another
 # one for llvm+clang+... using the same sources.
 set(LLVM_ALL_PROJECTS "clang;clang-tools-extra;compiler-rt;debuginfo-tests;libc;libclc;libcxx;libcxxabi;libunwind;lld;lldb;mlir;openmp;parallel-libs;polly;pstl")
+# The flang project is not yet part of "all" projects (see C++ requirements)
+set(LLVM_EXTRA_PROJECTS "flang")
+# List of all known projects in the mono repo
+set(LLVM_KNOWN_PROJECTS "${LLVM_ALL_PROJECTS};${LLVM_EXTRA_PROJECTS}")
 set(LLVM_ENABLE_PROJECTS "" CACHE STRING
-	"Semicolon-separated list of projects to build (${LLVM_ALL_PROJECTS}), or \"all\".")
+	"Semicolon-separated list of projects to build (${LLVM_KNOWN_PROJECTS}), or \"all\".")
 if( LLVM_ENABLE_PROJECTS STREQUAL "all" )
   set( LLVM_ENABLE_PROJECTS ${LLVM_ALL_PROJECTS})
 endif()
@@ -89,7 +93,7 @@
 
 if (LLVM_ENABLE_PROJECTS_USED OR NOT LLVM_ENABLE_PROJECTS STREQUAL "")
   set(LLVM_ENABLE_PROJECTS_USED ON CACHE BOOL "" FORCE)
-  foreach(proj ${LLVM_ALL_PROJECTS} ${LLVM_EXTERNAL_PROJECTS})
+  foreach(proj ${LLVM_KNOWN_PROJECTS} ${LLVM_EXTERNAL_PROJECTS})
     string(TOUPPER "${proj}" upper_proj)
     string(REGEX REPLACE "-" "_" upper_proj ${upper_proj})
     if ("${proj}" IN_LIST LLVM_ENABLE_PROJECTS)
Index: llvm/tools/CMakeLists.txt
===================================================================
--- llvm/tools/CMakeLists.txt
+++ llvm/tools/CMakeLists.txt
@@ -37,6 +37,8 @@
 add_llvm_external_project(lld)
 add_llvm_external_project(lldb)
 add_llvm_external_project(mlir)
+# Flang depends on mlir, so place it afterward
+add_llvm_external_project(flang)
 
 # Automatically add remaining sub-directories containing a 'CMakeLists.txt'
 # file as external projects.