Right now when doing test builds with clang, we wind up getting an error
from two different definitions of CLANG_PREREQ() in the headers.

It might be that we can just rip one of these out, but for now I'm just
making one of them conditional.

Signed-off-by: Peter Jones <[email protected]>

This make target doesn't actually use any of the objects built by the
compiler, so there's no concern about using an untested compiler or
anything like that.

It doesn't really need the warnings to show either, and they're
obnoxious, so this commit takes them out for that build target.

Signed-off-by: Peter Jones <[email protected]>

In some cases the -Werror / -Wfoo / -Wno-foo / -Wno-error=foo bits
aren't propagating in a way that clang is happy with, so we get errors
about unused variables and the like in Cryptlib and OpenSSL.

We're never going to fix those nits in this tree, so this patch tries
even harder to make the compiler ignore them, or at least not end the
build with a benign error.

Signed-off-by: Peter Jones <[email protected]>

I use compile_commands.json with vim all the time, so it's better if it
doesn't break.

This adds it to CI builds to try to ensure that better.

Signed-off-by: Peter Jones <[email protected]>