[REG 5.12-5.13] CMake release builds link to Qt debug LIBs

With Qt 5.13.0 RC2, CMake-based projects seem to link to the debug version of certain Qt LIB files also when building in release. This triggers the following run-time error:

Debug Assertion Failed!

Program: C:\Dev\TestProject\Release\MyApp.exe
File: minkernel\crts\ucrt\src\appcrt\heap\debug_heap.cpp
Line: 904

Expression: _CrtIsValidHeapPointer(block)

The mis-linking seem to be triggered by usage of static Qt libraries like ActiveQt.

Reproducer project: https://github.com/forderud/Qt-CMake-HelloWorld/tree/5.13-cmake . The reproducer will link to Qt5AxBased.lib Qt5Widgetsd.lib Qt5Guid.lib Qt5Cored.lib also when building in release.

I unfortunately don't know exactly when this regression was introduced, but it must have been sometime after 5.12.