[clang] Only build c-index-test and apinotes-test when clang tests are included (llvm#151157)

Those programs are only used for testing, and it's used in tests that
are already guarded by CLANG_INCLUDE_TESTS in clang/CMakeLists.txt.

This change enables us to do builds with
LLVM_INSTALL_TOOLCHAIN_ONLY=OFF, and CLANG_INCLUDE_TESTS=OFF, which
contain the required files to build other bits of llvm-project
standalone, but do not include those unnecessary testing programs.

Author: DavidSpickett

clang/tools/CMakeLists.txt

@@ -2,7 +2,6 @@ create_subdirectory_options(CLANG TOOL)
 
 add_clang_subdirectory(diagtool)
 add_clang_subdirectory(driver)
-add_clang_subdirectory(apinotes-test)
 if(CLANG_ENABLE_CIR)
   add_clang_subdirectory(cir-opt)
   add_clang_subdirectory(cir-translate)
@@ -22,7 +21,10 @@ if(HAVE_CLANG_REPL_SUPPORT)
   add_clang_subdirectory(clang-repl)
 endif()
 
-add_clang_subdirectory(c-index-test)
+if(CLANG_INCLUDE_TESTS)
+  add_clang_subdirectory(c-index-test)
+  add_clang_subdirectory(apinotes-test)
+endif()
 
 add_clang_subdirectory(clang-refactor)
 # For MinGW/Cygwin we only enable shared library if LLVM_LINK_LLVM_DYLIB=ON.