Conditionalize RIPEMD references

This unconditionally includes RIPEMD, but it's the only place in the
Android source code base. Instead of restoring RIPEMD to OpenSSL, just
remove it here.

Change-Id: Ie949f64cef1cb7de39baae3f118f2188e663c875

mac.c

@@ -65,8 +65,10 @@ struct {
 #endif
 	{ "hmac-md5",			SSH_EVP, EVP_md5, 0, -1, -1 },
 	{ "hmac-md5-96",		SSH_EVP, EVP_md5, 96, -1, -1 },
+#ifdef HAVE_EVP_RIPEMD
 	{ "hmac-ripemd160",		SSH_EVP, EVP_ripemd160, 0, -1, -1 },
 	{ "hmac-ripemd160@openssh.com",	SSH_EVP, EVP_ripemd160, 0, -1, -1 },
+#endif
 	{ "umac-64@openssh.com",	SSH_UMAC, NULL, 0, 128, 64 },
 	{ NULL,				0, NULL, 0, -1, -1 }
 };

myproposal.h

@@ -84,13 +84,19 @@
 #else
 # define SHA2_HMAC_MODES
 #endif
+#ifdef HAVE_EVP_RIPEMD
+#define	RIPEMD_MAC_MODES \
+	"hmac-ripemd160," \
+	"hmac-ripemd160@openssh.com,"
+#else
+# define RIPEMD_MAC_MODES
+#endif
 #define	KEX_DEFAULT_MAC \
 	"hmac-md5," \
 	"hmac-sha1," \
 	"umac-64@openssh.com," \
 	SHA2_HMAC_MODES \
-	"hmac-ripemd160," \
-	"hmac-ripemd160@openssh.com," \
+	RIPEMD_MAC_MODES \
 	"hmac-sha1-96," \
 	"hmac-md5-96"