package/llvm: add BPF backend

package/llvm: add BPF backend

bcc is a front-end tool for eBPF :
https://github.com/iovisor/bcc/blob/master/README.md.
eBPF is the most powerful Linux tracer, and bcc
allows to write eBPF scripts in C and PYTHON3.

BCC requires enabling LLVM backend BPF support.

Signed-off-by: Jugurtha BELKALEM <jugurtha.belkalem@smile.fr>
Signed-off-by: Romain Naour <romain.naour@gmail.com>
Tested-by: Qais Yousef <qais.yousef@arm.com>
Reviewed-by: Qais Yousef <qais.yousef@arm.com>
Cc: Qais Yousef <qais.yousef@arm.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>