Fix header include for handshake.

This should hopefully fix a build failure on the fuzzers.

Change-Id: If8db8dee768a83538cf37a65ec23c3f68f2be6a2
Reviewed-on: https://boringssl-review.googlesource.com/30264
Commit-Queue: Adam Langley <agl@google.com>
Reviewed-by: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

ssl/test/handshake_util.cc

diff --git a/ssl/test/handshake_util.cc b/ssl/test/handshake_util.cc
index 751ea34..62fbbf7 100644
--- a/ssl/test/handshake_util.cc
+++ b/ssl/test/handshake_util.cc
@@ -16,6 +16,7 @@
 
 #include <assert.h>
 #if defined(OPENSSL_LINUX) && !defined(OPENSSL_ANDROID)
+#include <errno.h>
 #include <fcntl.h>
 #include <spawn.h>
 #include <sys/socket.h>