diff -Naur clang-tools-extra-12.0.0rc1.src.orig/unittests/clang-tidy/CMakeLists.txt clang-tools-extra-12.0.0rc1.src/unittests/clang-tidy/CMakeLists.txt
--- clang-tools-extra-12.0.0rc1.src.orig/unittests/clang-tidy/CMakeLists.txt	2021-02-15 11:12:22.000000000 +0100
+++ clang-tools-extra-12.0.0rc1.src/unittests/clang-tidy/CMakeLists.txt	2021-02-15 17:02:32.000000000 +0100
@@ -1,9 +1,17 @@
 set(LLVM_LINK_COMPONENTS
   FrontendOpenMP
   Support
-  TestingSupport
   )
 
+if(CLANG_BUILT_STANDALONE)
+  # LLVMTestingSupport library is needed for clang-tidy tests.
+  if (EXISTS ${LLVM_MAIN_SRC_DIR}/lib/Testing/Support
+      AND NOT TARGET LLVMTestingSupport)
+    add_subdirectory(${LLVM_MAIN_SRC_DIR}/lib/Testing/Support
+      lib/Testing/Support)
+  endif()
+endif()
+
 get_filename_component(CLANG_LINT_SOURCE_DIR
   ${CMAKE_CURRENT_SOURCE_DIR}/../../clang-tidy REALPATH)
 include_directories(${CLANG_LINT_SOURCE_DIR})
@@ -37,6 +45,7 @@
   clangToolingCore
   clangTransformer
   )
+
 target_link_libraries(ClangTidyTests
   PRIVATE
   clangTidy
@@ -46,4 +55,5 @@
   clangTidyObjCModule
   clangTidyReadabilityModule
   clangTidyUtils
+  LLVMTestingSupport
   )