make benchmarks standalone

Most of our benchmarks rely on system dependencies such as zlib, etc
This has the following problems/limitations:

1. We're basically fuzzing not just the benchmark code, but benchmark code + dependencies. If we want to fuzz the dependencies, we should have a dedicated benchmark fo them. Example for zlib

2. The dependencies are not instrumented by the fuzzer during compilation because it uses system-installed libraries. This means if a fuzzer reaches dependency code, no feedback is received.

3. KLEE cannot handle external dependencies well: it needs all the code (besides libc) in one binary.

For these reasons, we should make benchmarks standalone, ie no dependent on other libraries as much as possible