Issue a deprecation warning on calls to `cmake_minimum_required` or
`cmake_policy` that set policies based on versions older than 3.10.
Note that the effective policy version includes `...<max>` treatment.
Update the check from commit 3a4791548d (Deprecate compatibility with
CMake versions older than 3.5, 2023-02-09, v3.27.0-rc1~508^2).
The OLD behaviors of all policies are deprecated, but only by
documentation. Add an explicit deprecation diagnostic for policies
introduced in CMake 3.9 and below to encourage projects to port away
from setting policies to OLD.
Add IPO support for Visual Studio (which is referred to by VS as
"Link Time Code Generation" and "Whole Program Optimization"), for
VS version >= 10. This allows CMake/VS users to enable IPO by setting
property `INTERPROCEDURAL_OPTIMIZATION`.
Fixes: #16748
We only define `INTERPROCEDURAL_OPTIMIZATION` behavior for C, CXX, and
Fortran languages. Do not try to enable support for other languages.
Furthermore, each language builds with a different compiler, so check
for support by CMake and the compiler for each language independently.
Fixes: #16944
Previously the `INTERPROCEDURAL_OPTIMIZATION` target property was
honored only for the Intel compiler on Linux and otherwise ignored. In
order to add support for more compilers incrementally without changing
behavior in the future, add a new policy whose NEW behavior enforces the
`INTERPROCEDURAL_OPTIMIZATION` property. Add flags for supported
compilers and otherwise produce an error.
