Merge #11286: [depends] Don't build libevent sample code

f38c05104 [depends] Don't build libevent sample code (fanquake)

Pull request description:

  Noticed today while doing Windows depends builds.
  Before and after libevent build on OS X.

  ```
  Building libevent...
    GEN      include/event2/event-config.h
  /Applications/Xcode.app/Contents/Developer/usr/bin/make  all-am
    CC       buffer.lo
    CC       bufferevent.lo
    CC       bufferevent_filter.lo
    CC       bufferevent_ratelim.lo
    CC       bufferevent_sock.lo
    CC       bufferevent_pair.lo
    CC       event.lo
    CC       evmap.lo
    CC       evthread.lo
    CC       evutil.lo
    CC       evutil_rand.lo
    CC       evutil_time.lo
    CC       listener.lo
    CC       log.lo
    CC       select.lo
    CC       poll.lo
    CC       kqueue.lo
    CC       signal.lo
    CC       evdns.lo
    CC       event_tagging.lo
    CC       evrpc.lo
    CC       http.lo
    CC       evthread_pthread.lo
    CC       sample/dns-example.o
    CC       sample/event-read-fifo.o
    CC       sample/hello-world.o
    CC       sample/http-server.o
    CC       sample/http-connect.o
    CC       sample/signal-test.o
    CC       sample/time-test.o
    CCLD     libevent_core.la
    CCLD     libevent_pthreads.la
    CCLD     libevent.la
    CCLD     libevent_extra.la
    CCLD     sample/event-read-fifo
    CCLD     sample/dns-example
    CCLD     sample/hello-world
    CCLD     sample/http-server
    CCLD     sample/http-connect
    CCLD     sample/signal-test
    CCLD     sample/time-test
  Staging libevent...
  ```

  ```
  Building libevent...
    GEN      include/event2/event-config.h
  /Applications/Xcode.app/Contents/Developer/usr/bin/make  all-am
    CC       buffer.lo
    CC       bufferevent.lo
    CC       bufferevent_filter.lo
    CC       bufferevent_pair.lo
    CC       bufferevent_ratelim.lo
    CC       bufferevent_sock.lo
    CC       event.lo
    CC       evmap.lo
    CC       evthread.lo
    CC       evutil.lo
    CC       evutil_rand.lo
    CC       evutil_time.lo
    CC       listener.lo
    CC       log.lo
    CC       select.lo
    CC       poll.lo
    CC       kqueue.lo
    CC       signal.lo
    CC       evdns.lo
    CC       event_tagging.lo
    CC       evrpc.lo
    CC       http.lo
    CC       evthread_pthread.lo
    CCLD     libevent_core.la
    CCLD     libevent_pthreads.la
    CCLD     libevent.la
    CCLD     libevent_extra.la
  Staging libevent...
  ```

Tree-SHA512: a82bde38e110a16f934c0f1e95d3ae66662c1b3c1367e4a6e7c4994f585ebeea4f5cbee4d98a8dc64a8e8936eb9f4bb0c55fb65e718f724d88e81cb8fa84be88

depends/packages/libevent.mk

@@ -9,7 +9,7 @@ define $(package)_preprocess_cmds
 endef
 
 define $(package)_set_vars
-  $(package)_config_opts=--disable-shared --disable-openssl --disable-libevent-regress
+  $(package)_config_opts=--disable-shared --disable-openssl --disable-libevent-regress --disable-samples
   $(package)_config_opts_release=--disable-debug-mode
   $(package)_config_opts_linux=--with-pic
 endef