Chez Scheme: repair to support vfasl boot in Rosetta

When Rosetta 2 runs x86_64 code, it doesn't enforce W^X, but the
`read` system call still refuses to write into executable memory.

racket/src/ChezScheme/c/version.h

@@ -329,6 +329,9 @@ typedef int tputsputcchar;
 # define S_ENABLE_CODE_WRITE(on) pthread_jit_write_protect_np(!(on))
 # define CANNOT_READ_DIRECTLY_INTO_CODE
 # include <pthread.h>
+#elif defined(__x86_64__)
+/* needed to run under Rosetta2 on ARM Mac OS: */
+# define CANNOT_READ_DIRECTLY_INTO_CODE
 #endif
 #define LDEXP
 #define ARCHYPERBOLIC