Lagom: Pass -Wno-deprecated-copy to clang too

Due to Serenity's use of concepts, it now requires clang 10 or newer,
and clang 10 or newer both understands and requires
-Wno-deprecated-copy.

Meta/Lagom/CMakeLists.txt

@@ -1,10 +1,7 @@
 cmake_minimum_required (VERSION 3.0)
 project (Lagom)
 
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -O2 -Wall -Wextra -Werror -std=c++2a -fPIC -g")
-if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
- set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-deprecated-copy")
-endif()
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -O2 -Wall -Wextra -Werror -std=c++2a -fPIC -g -Wno-deprecated-copy")
 
 if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wconsumed -Wno-overloaded-virtual")