[webkit-dev] Drop x86 (32bit) JIT backend

Hello all, Now, Xcode no longer has ability to build 32bit binary. Fedora starts dropping x86 32bit kernel shipping. Our x86/x86_64 JIT requires SSE2, so such CPUs can use JIT if they want by switching x86 to x86_64. And these CPUs are modern enough to run CLoop at high speed. x86 32bit JIT backend is very complicated and is being a major maintenance burden. This is due to very few # of registers. Which scatters a lot of isX86 / CPU(X86) in Baseline, DFG, and Yarr. I’m now planning to optimize some part of Yarr, but x86 YarrJIT is being a major barrier of such cleanups / optimizations. So, I would like to propose dropping X86 32bit JIT support. -Yusuke