FreeBSD installs both LLVM and gcc with tools named after the
major version, in the form "clang<major>", such as "clang16".
Detect compilers named this way, and find the related toolchain
tools.
Our `find_program` calls specify `HINTS` to look in the toolchain's
directory first, and then in `PATH`. `CMAKE_PREFIX_PATH` may be
specified by the user to help find packages for project dependencies,
but this should not override the binutils.
Fixes: #22512
Debian renames all LLVM/Clang binaries with a version suffix to allow
multiple versions to be installed at the same time. While there is a
version-agnostic package that adds a symlink to provide the standard
binary names, if only the versioned packages are installed, binaries
must be found as `binary-x.y`. In any case, using the same version of
the `binutils` as the compiler seems better.
