tree 1e837d6bb039320c6f38c60b69c9439abc720e5f
parent f621e7fa5df8d35cc379f9f7825f3d75b8489876
author Brad King <brad.king@kitware.com> 1554917921 -0400
committer Brad King <brad.king@kitware.com> 1555513244 -0400

MSVC: Add abstraction for runtime library selection

Replace our hard-coded defaults for `/MD` and `/MDd` with a first-class
abstraction to select the runtime library from an enumeration of logical
names.  We've long hesitated to do this because the idea of "runtime
library selection" touches on related concepts on several platforms.
Avoid that scope creep by simply defining an abstraction that applies
only when targeting the MSVC ABI on Windows.

Removing the old default flags requires a policy because existing
projects may rely on string processing to edit them and choose a runtime
library under the old behavior.  Add policy CMP0091 to provide
compatibility.

Fixes: #19108