Bug#472574: jack support should be enabled for AMD64

[Peter (p2) De Schrijver]

Package: portaudio19
Severity: normal

The memory barrier instructions for i386 (mfence, lfence and sfence) also work on 
amd64. So there is no reason to prohibit the use of jack.

-- System Information:
Debian Release: lenny/sid
  APT prefers unstable
  APT policy: (500, 'unstable')
Architecture: amd64 (x86_64)

Kernel: Linux 2.6.24.2 (SMP w/4 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash