MIPS: Fix clz implementation of the simulator.

MIPS: Fix clz implementation of the simulator.

BUG=

[kilvadyb, 2014-02-20 12:08:13]

On 2014/02/20 11:56:35, kilvadyb wrote:

Please check if using CompilerIntrinsics::CountLeadingZeros() instead of
__builtin_clz() is a good idea.

[Paul Lind, 2014-02-20 17:13:44]

> Please check if using CompilerIntrinsics::CountLeadingZeros() instead of
> __builtin_clz() is a good idea.

I see no harm in doing that, and it is probably a bit cleaner than using the
gcc-specific version in our code. (Though we make no attempt to build on MSVC.)

LGTM.

[Paul Lind, 2014-02-20 21:06:24]

Committed as r19517.