Issue a deprecation warning on calls to `cmake_minimum_required` or
`cmake_policy` that set policies based on versions older than 3.5.
Note that the effective policy version includes `...<max>` treatment.
Update the check from commit 5845c218d7 (Deprecate compatibility with
CMake versions older than 2.8.12, 2020-06-12, v3.19.0-rc1~629^2).
On AIX, symbols in executables must be exported in order to be visible
to modules (plugins) they load via `dlopen`. Prior to policy `CMP0065`,
CMake linked all executables with flags to export symbols, but the NEW
behavior for that policy is to do so only for executables that have the
`ENABLE_EXPORTS` target property set. In both cases, CMake has always
used the AIX linker option `-bexpall` option to export symbols from
executables.
This has worked fairly well with the XL compiler, but with the GNU
compiler it works only for C ABI symbols. The reason is that `-bexpall`
does not export symbols starting in `_` but the GNU C++ ABI mangles all
symbols with a leading `_`. Therefore we have only supported C ABI
plugins with the GNU compiler on AIX. Some projects have tried to work
around this by replacing `-bexpall` with `-bexpfull`, but the latter
often exports symbols that we do not want exported.
Avoid using `-bexpall` for executables by instead using by our own
internal `ExportImportList` script to compute symbol export lists from
the object files to be linked into an executable. Pass the explicitly
computed export list to the AIX linker's `-bE:...` option. We already
do this for shared object exports.
Issue: #19163
