user-native-test-3: Support cross-compiling for windows using cmake

When building with TCC, it needs to be a cross-compiler, and
present as ${CMAKE_CURRENT_BINARY_DIR}/cross-tcc

To compile for 64-bit windows:
$mkdir build
$cd build
$cmake ../make -DR3_OS_ID=0.3.40 -DCMAKE_TOOLCHAIN_FILE=../make/Toolchain-cross-mingw64-linux.cmake