Add 64-bit compare + branch for SPARC v9.

The same compare instruction is used for 32-bit and 64-bit compares. It
sets two different sets of flags: icc and xcc.

This patch adds a conditional branch instruction using the xcc flags for
64-bit compares.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178621 91177308-0d34-0410-b5e6-96231b3b80d8