Fix the compilation error in llvm_mode when using make clean all

[waugustus]

When executing the command make clean all in the llvm_mode directory, an error occurs during the test_build phase (as indicated in the Makefile). The error message is as follows:

unset AFL_USE_ASAN AFL_USE_MSAN AFL_INST_RATIO; AFL_QUIET=1 AFL_PATH=. AFL_CC=clang ../afl-clang-fast -O3 -funroll-loops -Wall -D_FORTIFY_SOURCE=2 -g -Wno-pointer-sign -DAFL_PATH=\"/usr/local/lib/afl\" -DBIN_PATH=\"/usr/local/bin\" -DVERSION=\"2.51b\"  ../test-instr.c -o test-instr 
echo 0 | ../afl-showmap -m none -q -o .test-instr0 ./test-instr
echo 1 | ../afl-showmap -m none -q -o .test-instr1 ./test-instr

Oops, the instrumentation does not seem to be behaving correctly!

Please ping <lcamtuf@google.com> to troubleshoot the issue.

Note that this error doesn't impact the proper functioning of afl-clang-fast.

To resolve this issue, I made the necessary modifications to the code based on the changes made in the latest version of the Makefile in the google/AFL repository (link)