Utilities/Release: Select MSVC runtime library via abstraction

Use the `CMAKE_MSVC_RUNTIME_LIBRARY` abstraction added by CMake 3.15
instead of hard-coding the `-MT` flag.

Utilities/Release/win32_release.cmake

@@ -28,8 +28,7 @@ CMAKE_Fortran_COMPILER:FILEPATH=FALSE
 CMAKE_GENERATOR:INTERNAL=Ninja
 BUILD_QtDialog:BOOL=TRUE
 CMake_GUI_DISTRIBUTE_WITH_Qt_LGPL:STRING=3
-CMAKE_C_FLAGS_RELEASE:STRING=-MT -O2 -Ob2 -DNDEBUG
-CMAKE_CXX_FLAGS_RELEASE:STRING=-MT -O2 -Ob2 -DNDEBUG
+CMAKE_MSVC_RUNTIME_LIBRARY:STRING=MultiThreaded$<$<CONFIG:Debug>:Debug>
 CMAKE_EXE_LINKER_FLAGS:STRING=-machine:x86 -subsystem:console,6.01
 CMake_QT_STATIC_QWindowsIntegrationPlugin_LIBRARIES:STRING=${qt_win_libs}
 CMAKE_PREFIX_PATH:STRING=${qt_prefix}

Utilities/Release/win64_release.cmake

@@ -28,8 +28,7 @@ CMAKE_Fortran_COMPILER:FILEPATH=FALSE
 CMAKE_GENERATOR:INTERNAL=Ninja
 BUILD_QtDialog:BOOL=TRUE
 CMake_GUI_DISTRIBUTE_WITH_Qt_LGPL:STRING=3
-CMAKE_C_FLAGS_RELEASE:STRING=-MT -O2 -Ob2 -DNDEBUG
-CMAKE_CXX_FLAGS_RELEASE:STRING=-MT -O2 -Ob2 -DNDEBUG
+CMAKE_MSVC_RUNTIME_LIBRARY:STRING=MultiThreaded$<$<CONFIG:Debug>:Debug>
 CMAKE_EXE_LINKER_FLAGS:STRING=-machine:x64 -subsystem:console,6.01
 CMake_QT_STATIC_QWindowsIntegrationPlugin_LIBRARIES:STRING=${qt_win_libs}
 CMAKE_PREFIX_PATH:STRING=${qt_prefix}