fix clang-cl warning for /constexpr:steps500000000

[miyanyan]

on windows, there are Clang GNU CLI and CLang MSVC CLI, the Clang GNU CLI works fine, but CLang MSVC CLI doesn't have all the option as MSVC, it will generate these warnings:

[build] [18/178   0% :: 0.880] Building CXX object tests\CMakeFiles\testarray_asmapkey.dir\testarray_asmapkey.cpp.obj
[build] clang-cl: warning: argument unused during compilation: '/constexpr:steps500000000' [-Wunused-command-line-argument]
[build] [19/178   1% :: 1.066] Building CXX object tests\CMakeFiles\testQuat_constexpr.dir\testQuat_constexpr.cpp.obj
[build] clang-cl: warning: argument unused during compilation: '/constexpr:steps500000000' [-Wunused-command-line-argument]
[build] [20/178   1% :: 1.079] Building CXX object tests\CMakeFiles\testvec_asunordmapkey.dir\testvec_asunordmapkey.cpp.obj
[build] clang-cl: warning: argument unused during compilation: '/constexpr:steps500000000' [-Wunused-command-line-argument]

see https://cmake.org/cmake/help/latest/variable/CMAKE_LANG_COMPILER_FRONTEND_VARIANT.html, I update the cmake version to >= 3.14

[sebsjames]

This change looks fine. I'll merge once the CI completes.