diff --git a/flang/CMakeLists.txt b/flang/CMakeLists.txt
--- a/flang/CMakeLists.txt
+++ b/flang/CMakeLists.txt
@@ -7,8 +7,6 @@
 set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
 set(CMAKE_CXX_EXTENSIONS OFF)
 
-include(GNUInstallDirs)
-
 set(FLANG_SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR})
 
 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_BINARY_DIR AND NOT MSVC_IDE)
@@ -27,7 +25,14 @@
   message("Building Flang as a standalone project.")
   project(Flang)
   set(FLANG_STANDALONE_BUILD ON)
+else()
+  set(FLANG_STANDALONE_BUILD OFF)
+endif()
+
+# Must go below project(..)
+include(GNUInstallDirs)
 
+if (FLANG_STANDALONE_BUILD)
   set(FLANG_BINARY_DIR ${CMAKE_CURRENT_BINARY_DIR})
   if (NOT MSVC_IDE)
     set(LLVM_ENABLE_ASSERTIONS ${ENABLE_ASSERTIONS}
@@ -179,7 +184,6 @@
   endif()
 
 else()
-  set(FLANG_STANDALONE_BUILD OFF)
   option(FLANG_INCLUDE_TESTS
          "Generate build targets for the Flang unit tests."
          ${LLVM_INCLUDE_TESTS})
diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -10,8 +10,6 @@
 #===============================================================================
 cmake_minimum_required(VERSION 3.13.4)
 
-include(GNUInstallDirs)
-
 set(LLVM_COMMON_CMAKE_UTILS "${CMAKE_CURRENT_SOURCE_DIR}/../cmake")
 
 # Add path for custom modules
@@ -39,14 +37,17 @@
   # In a standalone build, we don't have llvm to automatically generate the
   # llvm-lit script for us.  So we need to provide an explicit directory that
   # the configurator should write the script into.
-  set(LIBCXX_STANDALONE_BUILD 1)
+  set(LIBCXX_STANDALONE_BUILD TRUE)
   set(LLVM_LIT_OUTPUT_DIR "${LIBCXX_BINARY_DIR}/bin")
+endif()
+
+# Must go below project(..)
+include(GNUInstallDirs)
 
+if (LIBCXX_STANDALONE_BUILD)
   # Find the LLVM sources and simulate LLVM CMake options.
   include(HandleOutOfTreeLLVM)
-endif()
 
-if (LIBCXX_STANDALONE_BUILD)
   find_package(Python3 COMPONENTS Interpreter)
   if(NOT Python3_Interpreter_FOUND)
     message(SEND_ERROR "Python3 not found. Python3 is required")
diff --git a/libcxxabi/CMakeLists.txt b/libcxxabi/CMakeLists.txt
--- a/libcxxabi/CMakeLists.txt
+++ b/libcxxabi/CMakeLists.txt
@@ -10,8 +10,6 @@
 
 cmake_minimum_required(VERSION 3.13.4)
 
-include(GNUInstallDirs)
-
 set(LLVM_COMMON_CMAKE_UTILS "${CMAKE_CURRENT_SOURCE_DIR}/../cmake")
 
 # Add path for custom modules
@@ -37,17 +35,21 @@
   set(PACKAGE_STRING "${PACKAGE_NAME} ${PACKAGE_VERSION}")
   set(PACKAGE_BUGREPORT "llvm-bugs@lists.llvm.org")
 
+  set(LIBCXXABI_STANDALONE_BUILD TRUE)
+
   # In a standalone build, we don't have llvm to automatically generate the
   # llvm-lit script for us.  So we need to provide an explicit directory that
   # the configurator should write the script into.
-  set(LIBCXXABI_STANDALONE_BUILD 1)
   set(LLVM_LIT_OUTPUT_DIR "${LIBCXXABI_BINARY_DIR}/bin")
+endif()
 
+# Must go below project(..)
+include(GNUInstallDirs)
+
+if (LIBCXXABI_STANDALONE_BUILD)
   # Find the LLVM sources and simulate LLVM CMake options.
   include(HandleOutOfTreeLLVM)
-endif()
 
-if (LIBCXXABI_STANDALONE_BUILD)
   find_package(Python3 COMPONENTS Interpreter)
   if(NOT Python3_Interpreter_FOUND)
     message(WARNING "Python3 not found, using python2 as a fallback")
diff --git a/libunwind/CMakeLists.txt b/libunwind/CMakeLists.txt
--- a/libunwind/CMakeLists.txt
+++ b/libunwind/CMakeLists.txt
@@ -8,8 +8,6 @@
 
 cmake_minimum_required(VERSION 3.13.4)
 
-include(GNUInstallDirs)
-
 set(LLVM_COMMON_CMAKE_UTILS "${CMAKE_CURRENT_SOURCE_DIR}/../cmake")
 
 # Add path for custom modules
@@ -30,21 +28,28 @@
   # linking.
   include(EnableLanguageNolink)
   project(libunwind LANGUAGES NONE)
-  llvm_enable_language_nolink(C CXX ASM)
 
   set(PACKAGE_NAME libunwind)
   set(PACKAGE_VERSION 14.0.0git)
   set(PACKAGE_STRING "${PACKAGE_NAME} ${PACKAGE_VERSION}")
   set(PACKAGE_BUGREPORT "llvm-bugs@lists.llvm.org")
 
+  set(LIBUNWIND_STANDALONE_BUILD TRUE)
+endif()
+
+# Must go below project(..)
+include(GNUInstallDirs)
+
+if(LIBUNWIND_STANDALONE_BUILD)
+  llvm_enable_language_nolink(C CXX ASM)
+
+  # Find the LLVM sources and simulate LLVM CMake options.
+  include(HandleOutOfTreeLLVM)
+
   # In a standalone build, we don't have llvm to automatically generate the
   # llvm-lit script for us.  So we need to provide an explicit directory that
   # the configurator should write the script into.
-  set(LIBUNWIND_STANDALONE_BUILD 1)
   set(LLVM_LIT_OUTPUT_DIR "${LIBUNWIND_BINARY_DIR}/bin")
-
-  # Find the LLVM sources and simulate LLVM CMake options.
-  include(HandleOutOfTreeLLVM)
 else()
   set(LLVM_LIT "${CMAKE_SOURCE_DIR}/utils/lit/lit.py")
 endif()
diff --git a/lld/CMakeLists.txt b/lld/CMakeLists.txt
--- a/lld/CMakeLists.txt
+++ b/lld/CMakeLists.txt
@@ -1,12 +1,16 @@
 cmake_minimum_required(VERSION 3.13.4)
 
-include(GNUInstallDirs)
-
 # If we are not building as a part of LLVM, build LLD as an
 # standalone project, using LLVM as an external library:
 if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
   project(lld)
+  set(LLD_BUILT_STANDALONE TRUE)
+endif()
 
+# Must go below project(..)
+include(GNUInstallDirs)
+
+if(LLD_BUILT_STANDALONE)
   set(CMAKE_INCLUDE_CURRENT_DIR ON)
 
   # Rely on llvm-config.
@@ -140,8 +144,6 @@
   if(LLVM_HAVE_LIBXAR)
     set(XAR_LIB xar)
   endif()
-
-  set(LLD_BUILT_STANDALONE TRUE)
 endif() # standalone
 
 set(LLD_SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR})
diff --git a/lldb/CMakeLists.txt b/lldb/CMakeLists.txt
--- a/lldb/CMakeLists.txt
+++ b/lldb/CMakeLists.txt
@@ -1,7 +1,5 @@
 cmake_minimum_required(VERSION 3.13.4)
 
-include(GNUInstallDirs)
-
 # Add path for custom modules.
 set(CMAKE_MODULE_PATH
   ${CMAKE_MODULE_PATH}
@@ -13,6 +11,13 @@
 # using LLVM as an external library.
 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
   project(lldb)
+  set(LLDB_BUILT_STANDALONE TRUE)
+endif()
+
+# Must go below project(..)
+include(GNUInstallDirs)
+
+if(LLDB_BUILT_STANDALONE)
   include(LLDBStandalone)
 
   set(CMAKE_CXX_STANDARD 14 CACHE STRING "C++ standard to conform to")
diff --git a/lldb/cmake/modules/LLDBStandalone.cmake b/lldb/cmake/modules/LLDBStandalone.cmake
--- a/lldb/cmake/modules/LLDBStandalone.cmake
+++ b/lldb/cmake/modules/LLDBStandalone.cmake
@@ -108,5 +108,3 @@
 set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
 set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX})
 set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX})
-
-set(LLDB_BUILT_STANDALONE 1)
diff --git a/lldb/tools/debugserver/CMakeLists.txt b/lldb/tools/debugserver/CMakeLists.txt
--- a/lldb/tools/debugserver/CMakeLists.txt
+++ b/lldb/tools/debugserver/CMakeLists.txt
@@ -2,7 +2,12 @@
 
 project(Debugserver LANGUAGES C CXX ASM-ATT)
 
+# Must go below project(..)
+include(GNUInstallDirs)
+
 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
+  set(LLDB_BUILT_STANDALONE TRUE)
+
   set(CMAKE_MODULE_PATH
     ${CMAKE_MODULE_PATH}
     "${CMAKE_SOURCE_DIR}/../../cmake"
diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
--- a/llvm/CMakeLists.txt
+++ b/llvm/CMakeLists.txt
@@ -2,8 +2,6 @@
 
 cmake_minimum_required(VERSION 3.13.4)
 
-include(GNUInstallDirs)
-
 # CMP0116: Ninja generators transform `DEPFILE`s from `add_custom_command()`
 # New in CMake 3.20. https://cmake.org/cmake/help/latest/policy/CMP0116.html
 if(POLICY CMP0116)
@@ -47,6 +45,9 @@
   VERSION ${LLVM_VERSION_MAJOR}.${LLVM_VERSION_MINOR}.${LLVM_VERSION_PATCH}
   LANGUAGES C CXX ASM)
 
+# Must go after project(..)
+include(GNUInstallDirs)
+
 set(CMAKE_CXX_STANDARD 14 CACHE STRING "C++ standard to conform to")
 set(CMAKE_CXX_STANDARD_REQUIRED YES)
 if (CYGWIN)
diff --git a/mlir/CMakeLists.txt b/mlir/CMakeLists.txt
--- a/mlir/CMakeLists.txt
+++ b/mlir/CMakeLists.txt
@@ -1,10 +1,15 @@
 # MLIR project.
 
-include(GNUInstallDirs)
-
 # Check if MLIR is built as a standalone project.
 if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
   project(mlir)
+  set(MLIR_STANDALONE_BUILD TRUE)
+endif()
+
+# Must go below project(..)
+include(GNUInstallDirs)
+
+if(MLIR_STANDALONE_BUILD)
   cmake_minimum_required(VERSION 3.13.4)
 
   find_package(LLVM CONFIG REQUIRED)
diff --git a/polly/CMakeLists.txt b/polly/CMakeLists.txt
--- a/polly/CMakeLists.txt
+++ b/polly/CMakeLists.txt
@@ -1,10 +1,14 @@
-include(GNUInstallDirs)
-
 # Check if this is a in tree build.
 if (NOT DEFINED LLVM_MAIN_SRC_DIR)
   project(Polly)
   cmake_minimum_required(VERSION 3.13.4)
+  set(POLLY_STANDALONE_BUILD TRUE)
+endif()
+
+# Must go below project(..)
+include(GNUInstallDirs)
 
+if(POLLY_STANDALONE_BUILD)
   # Where is LLVM installed?
   find_package(LLVM CONFIG REQUIRED)
   set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} ${LLVM_CMAKE_DIR})
diff --git a/pstl/CMakeLists.txt b/pstl/CMakeLists.txt
--- a/pstl/CMakeLists.txt
+++ b/pstl/CMakeLists.txt
@@ -7,8 +7,6 @@
 #===----------------------------------------------------------------------===##
 cmake_minimum_required(VERSION 3.13.4)
 
-include(GNUInstallDirs)
-
 set(PARALLELSTL_VERSION_FILE "${CMAKE_CURRENT_SOURCE_DIR}/include/pstl/internal/pstl_config.h")
 file(STRINGS "${PARALLELSTL_VERSION_FILE}" PARALLELSTL_VERSION_SOURCE REGEX "#define _PSTL_VERSION .*$")
 string(REGEX REPLACE "#define _PSTL_VERSION (.*)$" "\\1" PARALLELSTL_VERSION_SOURCE "${PARALLELSTL_VERSION_SOURCE}")
@@ -18,6 +16,9 @@
 
 project(ParallelSTL VERSION ${VERSION_MAJOR}.${VERSION_MINOR}.${VERSION_PATCH} LANGUAGES CXX)
 
+# Must go below project(..)
+include(GNUInstallDirs)
+
 set(PSTL_PARALLEL_BACKEND "serial" CACHE STRING "Threading backend to use. Valid choices are 'serial', 'omp', and 'tbb'. The default is 'serial'.")
 set(PSTL_HIDE_FROM_ABI_PER_TU OFF CACHE BOOL "Whether to constrain ABI-unstable symbols to each translation unit (basically, mark them with C's static keyword).")
 set(_PSTL_HIDE_FROM_ABI_PER_TU ${PSTL_HIDE_FROM_ABI_PER_TU}) # For __pstl_config_site