Add handshaker as run_tests dependency.

Change-Id: I545a61794d6dbb187d973351da6d54e33a608d0d
Reviewed-on: https://boringssl-review.googlesource.com/30244
Reviewed-by: Matt Braithwaite <mab@google.com>

ssl/test/CMakeLists.txt

diff --git a/ssl/test/CMakeLists.txt b/ssl/test/CMakeLists.txt
index 8d9aa07..425b43b 100644
--- a/ssl/test/CMakeLists.txt
+++ b/ssl/test/CMakeLists.txt
@@ -32,4 +32,7 @@
   )
 
   target_link_libraries(handshaker ssl crypto)
+else()
+  # Declare a dummy target for run_tests to depend on.
+  add_custom_target(handshaker)
 endif()