Compiling libxcb-1.9.3 on AIX leads to this compiler error (occurs on multiple line numbers):
/tools/haubi/gentoo/sauxz6/var/tmp/portage/x11-libs/libxcb-1.9.3-r1/work/libxcb-1.9.3/src/xcb_in.c: In function 'get_event':
/tools/haubi/gentoo/sauxz6/var/tmp/portage/x11-libs/libxcb-1.9.3-r1/work/libxcb-1.9.3/src/xcb_in.c:339: error: '_xcb_in' has no member named 'reqevents'

While the declaration itself actually is:
  typedef struct _xcb_in {
    ...
    struct event_list *events;
    ...
  } _xcb_in;

Now, <sys/poll.h> does "#define events reqevents", so this is where the name 'reqevents' comes from.

However, in xcb_in.c, <sys/poll.h> is included /after/ "xcbint.h", so the struct _xcb_in declaration itself does not have 'events' redefined yet, while the code later in xcb.in.c does have.