Compile bpf module without relying on the current working directory of the process

Is it possible to compile a bpf module without relying on the current working directory of the process? I notice a comment [here](https://github.com/iovisor/bcc/blob/master/src/cc/frontends/clang/loader.cc#L161) stating that clang requires us to be inside the kernel source directory but is it possible to influence this and do a build without relying on relative paths (ie. without using chdir)?

Start at src/cc/frontends/clang/loader.cc, especially the comment around line 161, and trace how the BPF module compilation invokes clang and depends on the process working directory. Determine whether the relative-path requirement can be removed without chdir; done means documenting the constraint or defining and implementing a supported alternative, with validation identified from the surrounding code.

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