Log Message:
lang/sr: Mask x86_64 platforms

http://www.cs.arizona.edu/sr/impl.html:
"SR does not run on 64-bit X86/AMD64 Linux".

Indeed, the arch.h file has no provision for the x86_64 architecture.
NetBSD x86_64 gets past the trap because it patched the arch.h file to
alway define the arch.  Configuring on DragonFly64 illustrates the arch
is unsupported.