Fix the Linux shared build.

third_party/libevent/libevent.gyp

Index: third_party/libevent/libevent.gyp
===================================================================
--- third_party/libevent/libevent.gyp	(revision 26276)
+++ third_party/libevent/libevent.gyp	(working copy)
@@ -37,8 +37,18 @@
         # libevent has platform-specific implementation files.  Since its
         # native build uses autoconf, platform-specific config.h files are
         # provided and live in platform-specific directories.
-        [ 'OS == "linux"', { 'sources': [ 'epoll.c', 'epoll_sub.c' ],
-                             'include_dirs': [ 'linux' ] } ],
+        [ 'OS == "linux"', {
+          'sources': [ 'epoll.c', 'epoll_sub.c' ],
+          'include_dirs': [ 'linux' ],
+          'link_settings':
+            { 'libraries': [
+              # We need rt for clock_gettime().
+              # TODO(port) Maybe on FreeBSD as well?
+              '-lrt',
+              ],
+            },
+          }
+        ],
         [ 'OS == "mac" or OS == "freebsd"',   { 'sources': [ 'kqueue.c' ],
                              'include_dirs': [ 'mac' ] } ],
       ],