Roll AFL 2.31b:2.38b and switch coverage to use trace-pc-guard.

third_party/afl/src/Makefile

Index: third_party/afl/src/Makefile
diff --git a/third_party/afl/src/Makefile b/third_party/afl/src/Makefile
index e4072defae697b6c44e68a6929055cbe83b3944b..44d1ffa23f28efb771c8f97bd8e3f5f2f82ec761 100644
--- a/third_party/afl/src/Makefile
+++ b/third_party/afl/src/Makefile
@@ -123,7 +123,11 @@ install: all
 	install -m 755 $(PROGS) $(SH_PROGS) $${DESTDIR}$(BIN_PATH)
 	rm -f $${DESTDIR}$(BIN_PATH)/afl-as
 	if [ -f afl-qemu-trace ]; then install -m 755 afl-qemu-trace $${DESTDIR}$(BIN_PATH); fi
+ifndef AFL_TRACE_PC
 	if [ -f afl-clang-fast -a -f afl-llvm-pass.so -a -f afl-llvm-rt.o ]; then set -e; install -m 755 afl-clang-fast $${DESTDIR}$(BIN_PATH); ln -sf afl-clang-fast $${DESTDIR}$(BIN_PATH)/afl-clang-fast++; install -m 755 afl-llvm-pass.so afl-llvm-rt.o $${DESTDIR}$(HELPER_PATH); fi
+else
+	if [ -f afl-clang-fast -a -f afl-llvm-rt.o ]; then set -e; install -m 755 afl-clang-fast $${DESTDIR}$(BIN_PATH); ln -sf afl-clang-fast $${DESTDIR}$(BIN_PATH)/afl-clang-fast++; install -m 755 afl-llvm-rt.o $${DESTDIR}$(HELPER_PATH); fi
+endif
 	if [ -f afl-llvm-rt-32.o ]; then set -e; install -m 755 afl-llvm-rt-32.o $${DESTDIR}$(HELPER_PATH); fi
 	if [ -f afl-llvm-rt-64.o ]; then set -e; install -m 755 afl-llvm-rt-64.o $${DESTDIR}$(HELPER_PATH); fi
 	set -e; for i in afl-g++ afl-clang afl-clang++; do ln -sf afl-gcc $${DESTDIR}$(BIN_PATH)/$$i; done