ARM: Fix an issue with clang generating wrong code.
ARM: Fix an issue with clang generating wrong code.

Clang generated executables would enter the if condition when it wasn't
supposted to, resulting in the wrong simulated behavior.
Implementing the operation this way is a bit faster anyway.

LingxiaoJIA/gem5,haowu4682/gem5,haowu4682/gem5,LingxiaoJIA/gem5,LingxiaoJIA/gem5,haowu4682/gem5,LingxiaoJIA/gem5,haowu4682/gem5,haowu4682/gem5,LingxiaoJIA/gem5,haowu4682/gem5,haowu4682/gem5,haowu4682/gem5,LingxiaoJIA/gem5,haowu4682/gem5,LingxiaoJIA/gem5