cmake: use CMAKE_BUILD_TYPE=Release by default

CMakeLists.txt

@@ -98,6 +98,12 @@ ocv_cmake_hook(CMAKE_INIT)
 
 # must go before the project()/enable_language() commands
 ocv_update(CMAKE_CONFIGURATION_TYPES "Debug;Release" CACHE STRING "Configs" FORCE)
+if(NOT DEFINED CMAKE_BUILD_TYPE
+    AND NOT OPENCV_SKIP_DEFAULT_BUILD_TYPE
+)
+  message(STATUS "'Release' build type is used by default. Use CMAKE_BUILD_TYPE to specify build type (Release or Debug)")
+  set(CMAKE_BUILD_TYPE "Release" CACHE STRING "Choose the type of build")
+endif()
 if(DEFINED CMAKE_BUILD_TYPE)
   set_property(CACHE CMAKE_BUILD_TYPE PROPERTY STRINGS "${CMAKE_CONFIGURATION_TYPES}")
 endif()
@@ -599,10 +605,6 @@ endif()
 # ----------------------------------------------------------------------------
 # OpenCV compiler and linker options
 # ----------------------------------------------------------------------------
-# In case of Makefiles if the user does not setup CMAKE_BUILD_TYPE, assume it's Release:
-if(CMAKE_GENERATOR MATCHES "Makefiles|Ninja" AND "${CMAKE_BUILD_TYPE}" STREQUAL "")
-  set(CMAKE_BUILD_TYPE Release)
-endif()
 
 ocv_cmake_hook(POST_CMAKE_BUILD_OPTIONS)