Make ssl.h independent of ssl_ciphersuites.h

Previously, ssl.h included ssl_ciphersuites.h to have access to the
helper macros MBEDTLS_KEY_EXCHANGE_XXX_ENABLED, and for no other
reason. This commit moves the definitions of these macros to ssl.h,
thereby removing the dependency of ssl.h on ssl_ciphersuites.h.
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index ad60e82..c72bbeb 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -33,8 +33,6 @@
 #include "bignum.h"
 #include "ecp.h"
 
-#include "ssl_ciphersuites.h"
-
 #if defined(MBEDTLS_X509_CRT_PARSE_C)
 #include "x509_crt.h"
 #include "x509_crl.h"
@@ -402,6 +400,84 @@
 #define MBEDTLS_TLS_EXT_RENEGOTIATION_INFO      0xFF01
 
 /*
+ * Helper macros indicating whether certain classes
+ * of key exchanges are enabled in the configuration.
+ */
+
+/* Key exchanges using a certificate */
+#if defined(MBEDTLS_KEY_EXCHANGE_RSA_ENABLED)           || \
+    defined(MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED)       || \
+    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED)     || \
+    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED)   || \
+    defined(MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED)       || \
+    defined(MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED)      || \
+    defined(MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED)
+#define MBEDTLS_KEY_EXCHANGE__WITH_CERT__ENABLED
+#endif
+
+/* Key exchanges allowing client certificate requests */
+#if defined(MBEDTLS_KEY_EXCHANGE_RSA_ENABLED)           ||       \
+    defined(MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED)       ||       \
+    defined(MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED)      ||       \
+    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED)     ||       \
+    defined(MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED)    ||       \
+    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED)
+#define MBEDTLS_KEY_EXCHANGE__CERT_REQ_ALLOWED__ENABLED
+#endif
+
+/* Key exchanges involving server signature in ServerKeyExchange */
+#if defined(MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED)       || \
+    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED)     || \
+    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED)
+#define MBEDTLS_KEY_EXCHANGE__WITH_SERVER_SIGNATURE__ENABLED
+#endif
+
+/* Key exchanges using ECDH */
+#if defined(MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED)      || \
+    defined(MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED)
+#define MBEDTLS_KEY_EXCHANGE__SOME__ECDH_ENABLED
+#endif
+
+/* Key exchanges that don't involve ephemeral keys */
+#if defined(MBEDTLS_KEY_EXCHANGE_RSA_ENABLED)           || \
+    defined(MBEDTLS_KEY_EXCHANGE_PSK_ENABLED)           || \
+    defined(MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED)       || \
+    defined(MBEDTLS_KEY_EXCHANGE__SOME__ECDH_ENABLED)
+#define MBEDTLS_KEY_EXCHANGE__SOME_NON_PFS__ENABLED
+#endif
+
+/* Key exchanges that involve ephemeral keys */
+#if defined(MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED)       || \
+    defined(MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED)       || \
+    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED)     || \
+    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED)     || \
+    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED)   || \
+    defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
+#define MBEDTLS_KEY_EXCHANGE__SOME_PFS__ENABLED
+#endif
+
+/* Key exchanges using a PSK */
+#if defined(MBEDTLS_KEY_EXCHANGE_PSK_ENABLED)           || \
+    defined(MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED)       || \
+    defined(MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED)       || \
+    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
+#define MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED
+#endif
+
+/* Key exchanges using DHE */
+#if defined(MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED)       || \
+    defined(MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED)
+#define MBEDTLS_KEY_EXCHANGE__SOME__DHE_ENABLED
+#endif
+
+/* Key exchanges using ECDHE */
+#if defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED)     || \
+    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED)   || \
+    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
+#define MBEDTLS_KEY_EXCHANGE__SOME__ECDHE_ENABLED
+#endif
+
+/*
  * Size defines
  */
 #if !defined(MBEDTLS_PSK_MAX_LEN)
@@ -3915,6 +3991,8 @@
  */
 void mbedtls_ssl_session_free( mbedtls_ssl_session *session );
 
+#include "ssl_ciphersuites.h"
+
 #ifdef __cplusplus
 }
 #endif