[clangd][xpc] Fix XPC unittests

[jkorous]

Summary

Fix build after recent changes & add xpc unittests to check-clangd target.

[juliehockett]

This fixes the broken configure step on our bots now -- thanks for the quick patch!

clangd/test/CMakeLists.txt

 set(CLANGD_TEST_DEPS
   clangd
   ClangdTests
   # No tests for these, but we should still make sure they build.
   clangd-indexer
   dexp
   )
 
 if(CLANGD_BUILD_XPC)
   list(APPEND CLANGD_TEST_DEPS clangd-xpc-test-client)
+  list(APPEND CLANGD_TEST_DEPS ClangdXpcUnitTests)
 endif()
 
 foreach(dep FileCheck count not)
   if(TARGET ${dep})
     list(APPEND CLANGD_TEST_DEPS ${dep})
   endif()
 endforeach()
 
 configure_lit_site_cfg(
   ${CMAKE_CURRENT_SOURCE_DIR}/lit.cfg.in
   ${CMAKE_CURRENT_BINARY_DIR}/lit.cfg)
 
 add_lit_testsuite(check-clangd "Running the Clangd regression tests"
   ${CMAKE_CURRENT_BINARY_DIR}/../unittests;${CMAKE_CURRENT_BINARY_DIR}
   DEPENDS ${CLANGD_TEST_DEPS})

clangd/unittests/xpc/CMakeLists.txt

 set(LLVM_LINK_COMPONENTS
   support
   )
 
 get_filename_component(CLANGD_SOURCE_DIR
   ${CMAKE_CURRENT_SOURCE_DIR}/../../clangd REALPATH)
 include_directories(
   ${CLANGD_SOURCE_DIR}
   )
 
-add_extra_unittest(ClangdXpcTests
+add_custom_target(ClangdXpcUnitTests)
+add_unittest(ClangdXpcUnitTests ClangdXpcTests
   ConversionTests.cpp
   )
 
 target_link_libraries(ClangdXpcTests
   PRIVATE
   clangdXpcJsonConversions
   clangDaemon
   LLVMSupport
   LLVMTestingSupport
   )