CMake: Fix MSVC warning when using NMake

Fix warning: Command line warning D9025 : overriding '/W3' with '/W4'
Remove /W3, either via a regex or via new policy CMP0092 (CMake 3.15).

The policy has to be set before calling project(), otherwise the
CMAKE_<LANG>_FLAGS are already initialized.

See https://trac.wxwidgets.org/ticket/18438

CMakeLists.txt

@@ -23,10 +23,10 @@ if(APPLE AND NOT CMAKE_OSX_DEPLOYMENT_TARGET)
     set(CMAKE_OSX_DEPLOYMENT_TARGET 10.9 CACHE STRING "OS X Deployment Target")
 endif()
 
-project(wxWidgets)
-
 include(build/cmake/policies.cmake NO_POLICY_SCOPE)
 
+project(wxWidgets)
+
 # Initialize variables for quick access to wx root dir in sub dirs
 set(wxSOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR})
 set(wxBINARY_DIR ${CMAKE_BINARY_DIR})

build/cmake/functions.cmake

@@ -98,11 +98,15 @@ function(wx_set_common_target_properties target_name)
         ARCHIVE_OUTPUT_DIRECTORY "${wxOUTPUT_DIR}${wxPLATFORM_LIB_DIR}"
         RUNTIME_OUTPUT_DIRECTORY "${wxOUTPUT_DIR}${wxPLATFORM_LIB_DIR}"
         )
-    if(NOT wxCOMMON_TARGET_PROPS_DEFAULT_WARNINGS)
+
-        # Enable higher warnings for most compilers/IDEs
     if(MSVC)
-            target_compile_options(${target_name} PRIVATE /W4)
+        if(wxCOMMON_TARGET_PROPS_DEFAULT_WARNINGS)
+            set(MSVC_WARNING_LEVEL "/W3")
+        else()
+            set(MSVC_WARNING_LEVEL "/W4")
         endif()
+        target_compile_options(${target_name} PRIVATE ${MSVC_WARNING_LEVEL})
+    else()
         # TODO: add warning flags for other compilers
     endif()
 

build/cmake/init.cmake

@@ -57,6 +57,11 @@ if(MSVC)
         wx_string_append(CMAKE_C_FLAGS " /MP")
         wx_string_append(CMAKE_CXX_FLAGS " /MP")
     endif()
+
+    if(NOT POLICY CMP0092)
+        string(REGEX REPLACE "/W[0-4]" "" CMAKE_C_FLAGS "${CMAKE_C_FLAGS}")
+        string(REGEX REPLACE "/W[0-4]" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
+    endif()
 elseif(("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU") OR ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang"))
     if(wxBUILD_OPTIMISE)
         set(GCC_PREFERRED_RELEASE_FLAGS " -O2 -fomit-frame-pointer")

build/cmake/policies.cmake

@@ -58,3 +58,8 @@ if(POLICY CMP0072)
     # FindOpenGL prefers GLVND by default when available.
     cmake_policy(SET CMP0072 NEW)
 endif()
+
+if(POLICY CMP0092)
+    # MSVC warning flags are not in CMAKE_<LANG>_FLAGS by default
+    cmake_policy(SET CMP0092 NEW)
+endif()