CMake CMP0169: FetchContent_Populate is deprecated, call FetchContent_MakeAvailable instead

Summary

Since CMake 3.30, FetchContent_Populate is deprecated in favor of FetchContent_MakeAvailable.

Exact steps to reproduce

Try building GROMACS with CMake 3.30, observe the following warning:

CMake Warning (dev) at /usr/share/cmake-3.30/Modules/FetchContent.cmake:1953 (message):
  Calling FetchContent_Populate(muparser) is deprecated, call
  FetchContent_MakeAvailable(muparser) instead.  Policy CMP0169 can be set to
  OLD to allow FetchContent_Populate(muparser) to be called directly for now,
  but the ability to call it with declared details will be removed completely
  in a future version.
Call Stack (most recent call first):
  cmake/gmxManageMuparser.cmake:59 (FetchContent_Populate)
  src/gromacs/CMakeLists.txt:69 (gmx_manage_muparser)
This warning is for project developers.  Use -Wno-dev to suppress it.

In some cases, it is even a fatal error: https://gromacs.bioexcel.eu/t/cmake-error-at-usr-local-share-cmake-3-30-modules-fetchcontent-cmake-1951-message/10117

For developers: Why is this important?

We don't need extra CMake warnings.

Possible fixes

• 2024: set the policy to old
• 2025: use FetchContent_MakeAvailable