* Add the `-ffuzz` and `-fno-fuzz` CLI arguments.
* Detect fuzz testing flags from zig cc.
* Set the correct clang flags when fuzz testing is requested. It can be
combined with TSAN and UBSAN.
* Compilation: build fuzzer library when needed which is currently an
empty zig file.
* Add optforfuzzing to every function in the llvm backend for modules
that have requested fuzzing.
* In ZigLLVMTargetMachineEmitToFile, add the optimization passes for
sanitizer coverage.
* std.mem.eql uses a naive implementation optimized for fuzzing when
builtin.fuzz is true.
Tracked by #20702
