* Add -f(no-)sanitize-coverage-trace-pc-guard CLI flag which defaults to
  off. This value lowers to TracePCGuard = true (LLVM backend) and -Xclang
  -fsanitize-coverage-trace-pc-guard. These settings are not
  automatically included with -ffuzz.
* Add `Build.Step.Compile` flag for sanitize_coverage_trace_pc_guard
  with appropriate documentation.
* Add `zig cc` integration for the respective flags.
* Avoid crashing in ELF linker code when -ffuzz -femit-llvm-ir used
  together.