[Bug releng/32523] make stap buildable with clang/clang++

[Frank Ch. Eigler]

Hi -

>    I am nobody to say to you something, but if there were to be hosts
>    those lack boost_iostreams then there might be hosts where boost_system
>    could be absent, but the latter is strictly required by the build. So I
>    have a question why boost_iostreams is not treated as well as
>    boost_system

Yeah, I wonder that too. Yet nearly every sourceware buildbot slave
failed to build with the changes; it's not hypothetical. [1] :( Note
that we routinely build on as old an OS as RHEL8.  In the
boost::string_ref case, we have a #ifdef'd alternative implementation
for machines without those bits.  Maybe that's what we need.

[1] https://builder.sourceware.org/buildbot/#/builders?tags=%2Bsystemtap

>    The community is kindly requested to participate in the conversation

Yeah.  In general, we try to be generous at welcoming even partial
work patches into the tree, as long as they don't regress on our
normal fleet of builders.  If you/someone can get the code to that
state, I'd be happy to bring it back in.

- FChE