CMake: Fix installing to correct directory

Update path-style of CMAKE_INSTALL_PREFIX after the project is created, otherwise it might not be initialized

CMakeLists.txt

@@ -17,8 +17,6 @@ if(NOT CMAKE_CONFIGURATION_TYPES)
     endif()
 endif()
 
-file(TO_CMAKE_PATH "${CMAKE_INSTALL_PREFIX}" CMAKE_INSTALL_PREFIX)
-
 # https://blog.kitware.com/cmake-and-the-default-build-type/
 if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
     set(default_build_type "Debug")

build/cmake/main.cmake

@@ -9,6 +9,8 @@
 
 list(APPEND CMAKE_MODULE_PATH "${wxSOURCE_DIR}/build/cmake/modules")
 
+file(TO_CMAKE_PATH "${CMAKE_INSTALL_PREFIX}" CMAKE_INSTALL_PREFIX)
+
 include(build/cmake/files.cmake)            # Files list
 include(build/cmake/source_groups.cmake)    # Source group definitions
 include(build/cmake/functions.cmake)        # wxWidgets functions