clang-cl fails with cmake 3.17.2

[JohanMabille]

The azure-pipeline build pins cmake 3.14 to avoid failure when buiding with clang-cl. It seems that some options are not set correctly by cmake, this should be investigated so that we can use nay version of cmake.

[emmenlau]

For what its worth, we're using xsimd successfully with cmake 3.20 (current latest) with Visual Studio 2019 16.9.4 and clang-cl 11.