Fixes for LLVM 4.0 and python3

Fixes for LLVM 4.0 and python3

Avoid conflicting [no]inline attributes in function annotation. This was
probably always there but now 4.0 is treating this as an error.
Also, explicitly inline several functions in helpers.h.

Turn off unwind tables in the flags passed to clang. This was generating
calls to the elf relocator, which doesn't work for the BPF target. It is
unclear which change in LLVM 4.0 altered this behavior.

On python3, handle byte strings in the usual way for supporting
backwards compatibility.

Signed-off-by: Brenden Blanco <bblanco@gmail.com>