games/egl: unbreak the port's build against Clang 15

Add #include "x11_linux.h" to obtain the prototype for the
X11_GetAuxKeyRemapName() function, otherwise compiler does
not know its return value and defaults to `int':

unix/unix_glimp.c:117:5: error: incompatible integer
to pointer conversion assigning to 'char *' from 'int'
[-Wint-conversion]

Reported by: pkg-fallout