Use a more coherent naming for the options. This will help commonalise
the native case (e.g. NPTL on Linux, win32 on Windows), and add alternate
implementations (e.g. musl.)
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Bryan Hundven <bryanhundven@gmail.com>