No, it's not Sans Serif, it's Arial, just the bold-italic variant of
it. Try this:
M-: (face-font 'variable-pitch) RET
What do you see?
faces is preloaded, so it's not enough to recompile it. And w32 is
correct, since it should name the frame type (a.k.a. 'window-system')
value, not the system type.
You need to dump Emacs after byte-compiling faces.el.
--
Kaushal Modi