Description of problem:
Running `$ CC=/usr/bin/afl-clang-fast ./configure` results to:
configure: error: in `/home/nmavrogi/cvs/gnutls':
configure: error: C compiler cannot create executables
See `config.log' for more details

Checking config.log shows:
error: unable to load plugin '/usr/lib64/afl/afl-llvm-pass.so': '/usr/lib64/afl/afl-llvm-pass.so: undefined symbol: _ZTVN4llvm17GetElementPtrInstE'

Thus is seems like there is an ABI change in one of the c++ libs this was compiled.

How reproducible:
```
$ cat >c.c <<_EOF
int main() {
printf("hello\n");
}
_EOF

$ afl-clang-fast c.c
afl-clang-fast 2.49b by <lszekeres>
error: unable to load plugin '/usr/lib64/afl/afl-llvm-pass.so': '/usr/lib64/afl/afl-llvm-pass.so:
      undefined symbol: _ZTVN4llvm17GetElementPtrInstE'
```