Generic C++ templates/library for FreeBSD base

One of the projects I have been working on is converting ctld to C++ as
part of adding NVMeoF support.  Along the way I've written a few things
that I think are generic and would be useful in other parts of the base
system using C++.

One is a stringf() function that accepts printf() style format string and
arguments and returns a std::string.  I know C++23 adds <format>, but we
can't assume that yet, and this function is probably more useful when
adapting existing C code.  Compared to some other solutions, I chose to
wrap asprintf() and do an extra copy at the end into a std::string rather
than calling vsnprintf() twice.  It seems less ugly than the vsnprintf()
solutions also:

https://github.com/freebsd/freebsd-src/commit/01bd3d89ddf9ccbf884e52fe7289e8a9278e2d63

The other things I've added are a couple of unique_ptr<> wrappers that
use custom deleters.  One is malloc_up<> (I've copied a convention from
GDB of using a _up suffix for these) that uses free() as its deleter.
It's useful for things like strdup():

https://github.com/freebsd/freebsd-src/commit/a4f299fcad78be42a522aa26ec1cfddc5db986d8

The other is a FILE_up that wraps a FILE * and uses fclose() as its deleter
buried as part of a larger change:

https://github.com/freebsd/freebsd-src/commit/77b800022b18ab61983b22022b16943355b2bf75

I wonder if we don't instead want a standalone library for these sorts of
things, maybe a <freebsd> header with a freebsd namespace so that you'd have
freebsd::malloc_up<>, freebsd::stringf, etc.?  I'm not quite sure what to call
the library for bits that aren't just templates (such as the stringf
implementation).  I'm tempted to call it libutil++, but the mismatch with the header
name is a bit odd.

Thoughts?

-- 
John Baldwin