stdlib: reorder `add_subdirectory` to repair the Windows build
Due to the horrible attrocities against software of the attempt to perform
cross-compilation in the swift build system, we need to emulate the linking
behaviour for Windows with the link against the import library. The emulation
requires the custom creation of import library targets. In order to actually
get the linking semantics correct, the dependendency targets must be created
prior to use (unlike standard CMake). The reordering ensures that we get
correct linkage when building for Windows.
Perform a simple optimization to avoid a number of string comparisions for the
host system.
