configure: detect Windows Store builds based on the target OS
configure: detect Windows Store builds based on the target OS

These are the OS strings used with the MSVC toolchain and the upcoming LLVM
toolchain (https://github.com/mstorsjo/llvm-mingw/pull/30).

lu-zero/mfx_dispatch,lu-zero/mfx_dispatch,maximd33/mfx_dispatch,maximd33/mfx_dispatch