Compile with `-D_WIN32_WINNT=0x502` to use a WinXP-compatible API.
Compile with `-D_USING_V110_SDK71_` to tell the VS standard library
headers that we are building with a WinXP-compatible Windows SDK. Link
executables with `-subsystem:console,5.02` to make them runnable on
Windows XP 64-bit. Ideally `cmake-gui` should instead be linked with
`-subsystem:windows,5.02` but with the Ninja and Makefile generators
CMake adds `-subsystem:windows` after our `-subsystem:console,5.02` flag
and the linker seems to interpret this combination as we need.
Brad King