use "-O2 -DNDEBUG" in release by default in the case of MinGW

CMakeLists.txt

@@ -41,8 +41,11 @@ set(CMAKE_SHARED_LINKER_FLAGS_MINSIZEREL "" CACHE INTERNAL "" FORCE)
 set(CMAKE_SHARED_LINKER_FLAGS_RELWITHDEBINFO "" CACHE INTERNAL "" FORCE)
 set(CMAKE_VERBOSE OFF CACHE BOOL "Verbose mode")
 
-if (MINGW)
-    set(CMAKE_CXX_FLAGS_RELEASE "-O2 -DNDEBUG" CACHE STRING "")
+
+if (WIN32)
+    if(${CMAKE_GENERATOR} MATCHES "(MinGW)|(MSYS)")
+        set(CMAKE_CXX_FLAGS_RELEASE "-O2 -DNDEBUG" CACHE STRING "")
+    endif()
 endif()
 
 if(CMAKE_VERBOSE)