doc: use arch agnostic clang path in fuzzing doc (macOS)

Author: fanquake

doc/fuzzing.md

@@ -136,10 +136,10 @@ You may also need to take care of giving the correct path for `clang` and
 `clang++`, like `CC=/path/to/clang CXX=/path/to/clang++` if the non-systems
 `clang` does not come first in your path.
 
-Full configure that was tested on macOS Catalina with `brew` installed `llvm`:
+Full configure that was tested on macOS with `brew` installed `llvm`:
 
 ```sh
-./configure --enable-fuzz --with-sanitizers=fuzzer,address,undefined CC=/usr/local/opt/llvm/bin/clang CXX=/usr/local/opt/llvm/bin/clang++ --disable-asm
+./configure --enable-fuzz --with-sanitizers=fuzzer,address,undefined --disable-asm CC=$(brew --prefix llvm)/bin/clang CXX=$(brew --prefix llvm)/bin/clang++
 ```
 
 Read the [libFuzzer documentation](https://llvm.org/docs/LibFuzzer.html) for more information. This [libFuzzer tutorial](https://github.com/google/fuzzing/blob/master/tutorial/libFuzzerTutorial.md) might also be of interest.