build: Move epoll dependency check

DragonFly and OpenBSD rely on epoll-shim to provide eventfd.

Move the check for epoll dependency to the root meson.build script so
that we can use that for the <sys/evenfd.h> check as well.

This is preparation work for the following commits, no functional change
intended at this point.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1642>

meson.build

@@ -490,6 +490,12 @@ else
     build_dri2 = get_option('dri2') == 'true'
 endif
 
+if host_machine.system() in ['freebsd', 'openbsd']
+   epoll_dep = dependency('epoll-shim')
+else
+   epoll_dep = []
+endif
+
 have_eventfd = cc.has_header('sys/eventfd.h')
 if get_option('dri3') == 'auto'
     build_dri3 = dri3proto_dep.found() and xshmfence_dep.found() and libdrm_dep.found() and have_eventfd

present/meson.build

@@ -15,12 +15,6 @@ hdrs_present = [
     'present.h',
 ]
 
-if host_machine.system() in ['freebsd', 'openbsd']
-   epoll_dep = dependency('epoll-shim')
-else
-   epoll_dep = []
-endif
-
 libxserver_present = static_library('libxserver_present',
     srcs_present,
     include_directories: inc,