NMake Makefiles: Use Meson-style DLL and .lib naming if requested

To make things more consistent and less prone to confusion, if 'USE_MESON_LIBS'
is specified in the NMake command line, build the DLLs and .lib's that are
named like the Meson counterparts.  Binaries built with Meson+Visual Studio
and the ones that are built via NMake using 'USE_MESON_LIBS' are
interchangeable, provided that they are built with the same Visual Studio
version.