x32. Fixes jmp %reg in x32

x32 has 32-bit pointers; x86-64 can't jmp %r32. This patch addresses this issue by explicitly zero-extending brind's target to 64-bits.

Author: jpp

Reviewers: jfb, dschuff, pavel.v.chupin

Subscribers: llvm-commits

Differential revision: http://reviews.llvm.org/D12112

llvm-svn: 245452