Add server-side support for asynchronous signing.

The RSA key exchange needs decryption and is still unsupported.

Change-Id: I8c13b74e25a5424356afbe6e97b5f700a56de41f
Reviewed-on: https://boringssl-review.googlesource.com/5467
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/include/openssl/ssl3.h b/include/openssl/ssl3.h
index faf69ab..0694e56 100644
--- a/include/openssl/ssl3.h
+++ b/include/openssl/ssl3.h
@@ -634,6 +634,8 @@
 #define SSL3_ST_SW_CERT_B (0x141 | SSL_ST_ACCEPT)
 #define SSL3_ST_SW_KEY_EXCH_A (0x150 | SSL_ST_ACCEPT)
 #define SSL3_ST_SW_KEY_EXCH_B (0x151 | SSL_ST_ACCEPT)
+#define SSL3_ST_SW_KEY_EXCH_C (0x152 | SSL_ST_ACCEPT)
+#define SSL3_ST_SW_KEY_EXCH_D (0x153 | SSL_ST_ACCEPT)
 #define SSL3_ST_SW_CERT_REQ_A (0x160 | SSL_ST_ACCEPT)
 #define SSL3_ST_SW_CERT_REQ_B (0x161 | SSL_ST_ACCEPT)
 #define SSL3_ST_SW_SRVR_DONE_A (0x170 | SSL_ST_ACCEPT)