contrib: vulkan-loader: fix win32 building

The msys2 transforms everything into msys2 style DLLs but we should use the system vulkan-1.dll found in windows/system32.

We should also not patch the .def file to make it use the wrong DLL name.

The ASM handling was fixed in the previous patch.

The patches have been submitted upstream: https://github.com/KhronosGroup/Vulkan-Loader/pull/998

Plus some other cleanup when calling cmake.

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v3:

• update vulkan-headers/vulkan-loaders to use the merged patches
• rebase on top of !2528 (merged) for leaner build commands

v4:

• update the loader/headers versions to include upstream fixes
• rebase

v5:

• rebase

v6:

• rebase

v7:

• rebase

v8:

• modify vulkan.pc early

v9:

• rebase
• don't modify vulkan.pc early (done in !2595 (merged))