Use temporary files instead of piping in ebpf Makefile

[nnsee]

Currently, when compiling the eBPF module, in the Makefile, the output of clang is directly piped to llc. This is bad, because in this case, should clang fail, llc still runs, but produces faulty .o files. make never picks up on it and doesn't abort compilation - a success is reported across the board (apart from the clang log).

This patch removes the file and explicitly writes (and later deletes) clang's output to a .partial file. This is later used as the input of llc.

[gustavo-iniguez-goya]

thank you @nnsee :) everyone seems to use pipes, but it's true that empty/invalid objects was a problem.