Fix old-style definition warning for xf86OSInputThreadInit()

../hw/xfree86/os-support/stub/stub_init.c: In function ‘xf86OSInputThreadInit’:
../hw/xfree86/os-support/stub/stub_init.c:29:1: warning: old-style function definition [-Wold-style-definition]

(cherry picked from commit 7c266caf)
3 jobs for warning-fix-1.20 in 5 minutes and 4 seconds
Status Job ID Name Coverage
  Docker Image
passed #2014735
debian-testing

00:00:33

 
  Build And Test
passed #2014736
autotools-build-and-test

00:04:31

passed #2014737
meson-build-and-test

00:01:36