curve22519: Add a portable backend implemented in plain C

src/libstrongswan/plugins/curve25519/curve25519_drv.c

@@ -14,6 +14,7 @@
  */
 
 #include "curve25519_drv.h"
+#include "curve25519_drv_portable.h"
 
 typedef curve25519_drv_t*(*curve25519_drv_create)();
 
@@ -23,6 +24,7 @@ typedef curve25519_drv_t*(*curve25519_drv_create)();
 curve25519_drv_t *curve25519_drv_probe()
 {
 	curve25519_drv_create drivers[] = {
+		curve25519_drv_portable_create,
 	};
 	curve25519_drv_t *driver;
 	int i;