Chez Scheme: repair to support vfasl boot in Rosetta
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.

mflatt/ChezScheme,mflatt/ChezScheme,mflatt/ChezScheme