* ci: build the Windows x64 dependencies and slicer with clang-cl
Passes -l -x from the Windows jobs, using the clang-cl and Ninja options
added in #15373. Ninja runs each dependency's build step as a plain command,
so the jobs set up a VC environment for OpenSSL's nmake. arm64 stays on MSVC
for now.
The deps cache key gains the compiler, so windows-x64 becomes
windows-x64-clang and windows-arm64 becomes windows-arm64-msvc.
* deps: select OpenSSL's ARM64 target from DEPS_ARCH
CMAKE_GENERATOR_PLATFORM is only set by -A, which Ninja never receives, so
the Ninja build selected the x64 target on ARM64. DEPS_ARCH is derived from
CMAKE_SYSTEM_PROCESSOR and is already independent of the generator.
* ci: build the Windows ARM64 dependencies and slicer with clang-cl
Three dependencies need handling first. libpng and OpenCV each build an ARM
SIMD path that does not compile with clang-cl, so those paths are off; PNG
already had the same opt-out for Apple ARM. OCCT is built with cl, since
clang-cl cannot emit one of its large generated files and there is no option
to turn that off. All three are gated to Windows ARM64 with clang.
