Merge #19452: doc: afl fuzzing comment about afl-gcc and afl-g++

2b78a11 doc: afl fuzzing comment about afl-gcc and afl-g++ (nsa)

Pull request description:

  When trying to build the fuzz tests with `--enable-lcov` on a Ubuntu machine, noticed that the documentation was lacking with regards to the afl-gcc and afl-g++ options. `afl-clang-fast` and `afl-clang-fast++` in the examples just need to be replaced with `afl-gcc` and `afl-g++`. I also had to set the `-m` flag as well to get the fuzzers to run.

ACKs for top commit:
  practicalswift:
    ACK 2b78a11
  MarcoFalke:
    Concept ACK 2b78a11, haven't tested

Tree-SHA512: d8151afd79de949e8c6da49b69bbbf1470eb478c8ddcbc69b30e86bf9396c0f13835a655d4ae658f7dc4f36c35b02cd23b08358fb73a71e15bf14e76c1f365a4

Author: fanquake

doc/fuzzing.md

@@ -121,6 +121,8 @@ $ git clone https://github.com/google/afl
 $ make -C afl/
 $ make -C afl/llvm_mode/
 $ ./autogen.sh
+# It is possible to compile with afl-gcc and afl-g++ instead of afl-clang. However, running afl-fuzz
+# may require more memory via the -m flag.
 $ CC=$(pwd)/afl/afl-clang-fast CXX=$(pwd)/afl/afl-clang-fast++ ./configure --enable-fuzz
 $ make
 # For macOS you may need to ignore x86 compilation checks when running "make". If so,