Fix compilation with windows.h from latest w32api

misc.h has complex logic (checking MAXSHORT is undefined etc.)
controlling if it includes assert.h or not.

Including windows.h from w32api 9.0.0 now trips over that, causing
assert.h to not be included, causing various errors, e.g.

In file included from ../include/cursor.h:53,
                 from ../include/dix.h:54,
                 from ../os/osdep.h:139,
                 from ../hw/xwin/winauth.c:40:
../include/privates.h: In function ‘dixGetPrivateAddr’:
../include/privates.h:121:5: error: implicit declaration of function ‘assert’ [-Werror=implicit-function-declaration]

Fix this by IWYU in privates.h
5 jobs for include-assert-h in 4 minutes and 45 seconds (queued for 6 seconds)
Status Name Job ID Coverage
  Docker Image
passed debian-buster #13251258

00:00:16

 
  Build And Test
passed autotools #13251259

00:04:28

passed meson #13251260

00:01:53

passed meson-noglamor #13251261

00:01:12

passed mingw-cross-build #13251262

00:00:50