Changelog OG Kernel Rev 26

Changelog:

* Upstream and merge to v4.19.251

* Use O3 for Clang (AOSP ONLY)

* Adapt for compilation with SDClang 14.1.2 (AOSP ONLY)

* Compile with ld.lld llvm-as llvm-ar llvm-nm llvm-objcopy llvm-objdump llvm-strip (AOSP and MIUI)