Try to make old compilers happy, take 2
Try to make old compilers happy, take 2

It turned out not only structured bindings are C++17 feature that are
causing trouble, but also `return {a, b}` is C++17 only and fails even
on some LLVM7:

	https://github.com/iovisor/bpftrace/pull/423#issuecomment-465337004

Try to fix it by rewriting to construct return tuple explicitly.

iovisor/bpftrace,iovisor/bpftrace,iovisor/bpftrace,iovisor/bpftrace