Ed25519: add missing C++ directives for C functions

Assembly code has C function names.
Need to tell C++ that these are C function and not to mangle names.

wolfssl/wolfcrypt/ge_operations.h

@@ -70,6 +70,9 @@ typedef struct {
   ge T;
 } ge_p3;
 
+#ifdef __cplusplus
+    extern "C" {
+#endif
 
 WOLFSSL_LOCAL int  ge_compress_key(byte* out, const byte* xIn, const byte* yIn,
                                                                 word32 keySz);
@@ -122,6 +125,10 @@ void ge_add(ge_p1p1 *r, const ge_p3 *p, const ge_cached *q);
 void ge_sub(ge_p1p1 *r, const ge_p3 *p, const ge_cached *q);
 #endif
 
+#ifdef __cplusplus
+    }    /* extern "C" */
+#endif
+
 #endif /* HAVE_ED25519 */
 
 #endif /* WOLF_CRYPT_GE_OPERATIONS_H */