(regression introduced by 1644bdb7d2)
Setting a maximum version in cmake_minimum_required() effectively sets
the behavior to NEW for all policies introduced in all CMake versions up
to and including that maximum version. The NEW behavior for CMP0091,
introduced in CMake 3.15, uses CMake variables to specify the MSVC
runtime library against which to link, rather than placing the relevant
flags in CMAKE_C_FLAGS*. Thus, replacing /MD with /MT in CMAKE_C_FLAGS*
no longer has any effect when using CMake 3.15+.
17df25f92c