BPF ELF tools

Tools to operate on compiled ELF files for Superopt. Currently this repository consists of two tools: text extractor and ELF patcher. The text extractor is a tool for retrieving the instructions, map data, and relocation data from an ELF file. There are currently two text extractors; the old one uses bpf_load and the new one the libbpf repository (https://github.com/libbpf/libbpf). The old text extractor is obselete and doesn't work for files generated with newer versions of Clang; the libbpf text extractor in text-extractor should always be used. The ELF patcher replaces a current section in the ELF with a new sequence of instructions.