(trunk) don't link against -lrt unless libevent needs it

configure.ac

@@ -161,6 +161,15 @@ AC_TRY_LINK([#include <stdarg.h>], [va_list ap1, ap2; va_copy(ap1, ap2);],
 ])
 
 
+dnl libevent likes to link against librt if possible
+dnl for clock_gettime() and clock_settime()
+dnl TODO(libevent2): this can probably be removed after
+dnl we switch to libevent2, since it will have PKG_CONFIG
+AC_CHECK_LIB([rt],
+             [clock_gettime],
+             [libevent_extra_libs="-lrt"],
+             [libevent_extra_libs=""])
+
 dnl build our copy of libevent whether we use it or not,
 dnl because "make dist" needs its Makefiles to exist, and
 dnl AM_CONDITIONAL + AC_CONFIG_SUBDIRS don't seem to play nice
@@ -169,7 +178,7 @@ libevent_source=bundled
 AC_CHECK_LIB([event],[evutil_vsnprintf],
              [libevent_found=yes],
              [libevent_found=no],
-             [-levent])
+             [$libevent_extra_libs])
 AC_CHECK_HEADER([event-config.h],
                 [libevent_headers_found=yes],
                 [libevent_headers_found=no])
@@ -186,7 +195,7 @@ if test "x$libevent_source" = "xbundled"; then
     LIBEVENT_LIBS="\$(top_builddir)/third-party/libevent/libevent.la"
 else
     LIBEVENT_CFLAGS=""
-    LIBEVENT_LIBS="-levent -lrt"
+    LIBEVENT_LIBS="-levent $libevent_extra_libs"
 fi
 AC_SUBST(LIBEVENT_CFLAGS)
 AC_SUBST(LIBEVENT_LIBS)