Handle clang-cl warning settings the same as MSVC

Author: Flamefire

cmake/BoostAddWarnings.cmake

@@ -14,7 +14,14 @@ function(boost_add_warnings target level)
   if(NOT level IN_LIST allowed_levels)
     message(FATAL_ERROR "${level} is not a valid warning level (${allowed_levels})")
   endif()
-  if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU" OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
+  if(MSVC)
+    set(warn_off /W0)
+    set(warn_on /W3)
+    foreach(_lvl IN ITEMS all extra pedantic)
+      set(warn_${_lvl} /W4)
+    endforeach()
+    set(werror /WX)
+  elseif(CMAKE_CXX_COMPILER_ID STREQUAL "GNU" OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
     set(warn_off -w)
     set(warn_on  -Wall)
     set(warn_all -Wall)
@@ -27,13 +34,6 @@ function(boost_add_warnings target level)
       set(warn_${_lvl} -w1)
     endforeach()
     set(werror "")
-  elseif(MSVC)
-    set(warn_off /W0)
-    set(warn_on /W3)
-    foreach(_lvl IN ITEMS all extra pedantic)
-      set(warn_${_lvl} /W4)
-    endforeach()
-    set(werror /WX)
   endif()
   target_compile_options(${target} PRIVATE ${warn_${level}})
   if(warningsAsErrors)