Adds casts to zeroize functions to allow building as C++

library/cipher.c

@@ -51,7 +51,7 @@
 
 /* Implementation that should never be optimized out by the compiler */
 static void mbedtls_zeroize( void *v, size_t n ) {
-    volatile unsigned char *p = v; while( n-- ) *p++ = 0;
+    volatile unsigned char *p = (unsigned char*)v; while( n-- ) *p++ = 0;
 }
 
 static int supported_init = 0;