Bump MSVC required version to 19.14

LLVM passes overaligned objects by value, which MSVC 19.1 didn't support on
x86_32. MSVC added this support somewhere between 19.1 and 19.14, but godbolt
doesn't have 19.11, 19.12, or 19.13 so I can't test before 19.14:
https://gcc.godbolt.org/z/75YoEz

Even if users are using the Visual Studio 2017 series of Visual C++ toolchains,
they should've already updated to 19.14 or newer at this point, or they
wouldn't be able to build LLVM. This just raises the CMake required minimum
version so the build fails earlier.

Differential Revision: https://reviews.llvm.org/D92515