Fix Cygwin w32 build broken by last commit in w32font.c.

Fix Cygwin w32 build broken by last commit in w32font.c.

 src/w32font.c (w32_load_unicows_or_gdi32, get_outline_metrics_w)
 (get_text_metrics_w, get_glyph_outline_w, get_char_width_32_w)
 [!WINDOWSNT]: These functions are no longer compiled on Cygwin;
 they are replaced by macros that expand into direct calls to the
 corresponding functions from GDI32.DLL.
 (globals_of_w32font) [WINDOWSNT]: Don't initialize g_b_* static
 variables in the Cygwin build, they are unused.