* Drop CppBackend. It is removed.
Changelog:
* GCC ABI Tag
* LLVM IR: new intrinsics etc.
* Change LLVM IPO model
* Support ThinLTO
* Improve the ARM targets, ARMv8.2-A support etc.
* Improve the MIPS targets
* Improve the PowerPC target, default optim O3 to O2
* Improve the X86 target, SKylake AVX-512 etc.
* Improve the AMDGPU, better support for Mesa 12