This makes JitBaseBlockCache::ErasePhysicalRange around 50% faster and
PPCAnalyzer::Analyze around 40% faster. Rogue Squadron 2's notoriously
laggy action of switching to and from cockpit view is made something
like 20-30% faster by this, though this is a very rough measurement.
This is a very small libary, and as I understand it, it was more or less
developed for Dolphin.
This moves the two relevant files from Externals to Common, changes the
namespace to Common, reformats the code, and adds Dolphin copyright
notices. The change in copyright notice and license was approved by
AdmiralCurtiss.
JosJuice