sdk/bpf/c: support asm files

[riptl]

Problem

The BPF C SDK cannot compile asm (*.s) files.

Summary of Changes

Adds rules to bpf.mk to auto-detect *.s files and assemble them with clang.

Fixes #

[stale[bot]]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.

[riptl]

@jstarry Sorry for the ping, could you help me check if the team has any interest in reviewing this PR? I'm not sure who is maintaining the C SDK.

[jstarry]

I'm not sure who is maintaining the C SDK.

I'm not sure either, maybe @dmakarov?