ENH: use the new CMake mechanism to specify MSVC's static or DLL CRT

[dzenanz]

Related to #2872.

PR Checklist

• No API changes were made (or the changes have been approved)
• No major design changes were made (or the changes have been approved)
• Added test (or behavior not changed)
• Updated API documentation (or API not changed)
• Added license to new files (if any)
• Added Python wrapping to new files (if any) as described in ITK Software Guide Section 9.5
• Added ITK examples for all new major features (if any)

[dzenanz]

@MrTzschr, @liupeiqiHN and @tim-evain your opinion is welcome.

I have not tested to confirm that this fixes #2872. Tim, can you test and report?

[jhlegarreta]

Have not tried.

Does this happen on other OS?

[tim-evain]

@dzenanz
New variable ITK_MSVC_STATIC_RUNTIME_LIBRARY does correctly switch ITK config, but has no impact on underlying DCMTK configuration regarding #2872 (i.e. when off, DCMTK is still built with static CRT)

[dzenanz]

This needs an addition of passing this flag to external projects, such as DCMTK and Expat, but probably others, too.

[hjmjohnson]

@dzenanz Is this still a draft?

[dzenanz]

Yes. While this commit on its own is fine, some logical connected changes are needed to make this resolved, as I commented earlier.

[dzenanz]

@tim-evain I just updated this. Can you test now?

[tim-evain]

@dzenanz DCMTK is still built against static CRT when ITK_MSVC_STATIC_RUNTIME_LIBRARY is OFF.
I do see CMAKE_MSVC_RUNTIME_LIBRARY:STRING=MultiThreadedDLL in the CMakeCache of the external project build, but the compiler flags still have /MT(d). I'm not sure how that interacts with the property setting made by CMAKE_MSVC_RUNTIME_LIBRARY but I guess compiler flags overwrite that setting?

[dzenanz]

Policy 91 needs to be set to NEW for the CMAKE_MSVC_RUNTIME_LIBRARY to have an effect. The policy could be set manually, or by requiring minimum CMake version of 3.15 or higher. Otherwise compiler flags govern which CRT will be linked.

I guess DCMTK sets those flag somewhere, as it want to link to static CRT. And since it has CMP0091 implicitly as OLD, passed setting has no effect.

[dzenanz]

Even the latest DCMTK tops out at CMake 3.13.2.

[hjmjohnson]

I am not a windows expert, but all these changes appear reasonable.