!15387 move link dl to libevent's patch

From: @zhoufeng54
Reviewed-by: @kisnwang,@xu-yfei
Signed-off-by: @xu-yfei

cmake/external_libs/libevent.cmake

@@ -1,4 +1,4 @@
-set(libevent_CFLAGS "-fstack-protector-all -D_FORTIFY_SOURCE=2 -O2 -ldl")
+set(libevent_CFLAGS "-fstack-protector-all -D_FORTIFY_SOURCE=2 -O2")
 if(NOT CMAKE_SYSTEM_NAME MATCHES "Darwin")
     set(libevent_LDFLAGS "-Wl,-z,now")
 endif()
@@ -19,6 +19,7 @@ mindspore_add_pkg(libevent
         LIBS event event_pthreads event_core event_openssl
         URL ${REQ_URL}
         MD5 ${MD5}
+        PATCHES ${CMAKE_SOURCE_DIR}/third_party/patch/libevent/libevent.patch001
         CMAKE_OPTION -DCMAKE_BUILD_TYPE:STRING=Release -DBUILD_TESTING=OFF -DOPENSSL_ROOT_DIR:PATH=${openssl_ROOT})
 
 include_directories(${libevent_INC})

third_party/patch/libevent/libevent.patch001

@@ -0,0 +1,12 @@
+diff -Npur libevent/CMakeLists.txt libevent-modify/CMakeLists.txt
+--- libevent/CMakeLists.txt	2020-07-05 20:02:46.000000000 +0800
++++ libevent-modify/CMakeLists.txt	2021-04-19 16:36:57.982307500 +0800
+@@ -852,7 +852,7 @@ if (NOT EVENT__DISABLE_OPENSSL)
+ 
+     list(APPEND SRC_OPENSSL bufferevent_openssl.c)
+     list(APPEND HDR_PUBLIC include/event2/bufferevent_ssl.h)
+-    list(APPEND LIB_APPS ${OPENSSL_LIBRARIES})
++    list(APPEND LIB_APPS ${OPENSSL_LIBRARIES} -ldl)
+ endif()
+ 
+ if (NOT EVENT__DISABLE_THREAD_SUPPORT)