faf7d4fa86 build: Add cov_fuzz target (MarcoFalke)
fac71e364e build: link fuzz/test_runner.py for out-of-tree builds (MarcoFalke)
faf2c5aca0 build: Remove unused USE_COVERAGE (MarcoFalke)
Pull request description:
Only libFuzzer is supported right now, so clang is required. Thus, this needs a workaround such as https://github.com/bitcoin/bitcoin/issues/12602#issuecomment-562788247
Can be tested with:
```
mkdir build && cd build
../configure --enable-fuzz --with-sanitizers=fuzzer --enable-lcov --enable-lcov-branch-coverage CC=clang CXX=clang++
make $MAKEJOBS
make cov_fuzz
ACKs for top commit:
practicalswift:
ACK faf7d4fa86
Tree-SHA512: 6828f8f81d95f6781713d0b09d7eba2ffdb50217e09ca839db61791a4ed70024859c7a0cb01d9eede79166d574dd57ece01f9d9fe2610d4a72a4ca4a4ce0b838