WIP: do not hardcode the Windows SDK path

[AlessandroMenti]

Work in progress, do not merge

Introduce additional functions to avoid hardcoding the Windows SDK installation paths in portfiles.

[msftclas]

All CLA requirements met.

[AlessandroMenti]

First, apologies for the late reply as I've been quite busy lately.

While this patch works, I am not fully sure if this is the best way to detect an installation of the Windows SDK.

As it is, the CMake script:

1. tries to find a Windows 10 SDK, falling back to a Windows 8.1/8 SDK and, finally, to a Windows 7 SDK if more recent SDK versions are not found;
2. it assumes that the Windows SDK desired version is always specified in the WindowsSDKVersion environment variable, which might not be the case.

@ras0219-msft, @PhoebeHui and @voskrese, do you think it would be worthwhile to "generalize" the search approach as follows (on a similar note to what this FindWindowsSDK module does):

1. if the WindowsSDKDir and WindowsSDKVersion environment variables are set and correspond to a valid SDK installation path, use them;
2. else, try searching for a Windows 10/8.1/8/7.1 SDK installation in the Registry; in any case, specifying a minimum admissible version of the SDK should be allowed;
3. export the correct binary/include/library directories as CMake variables to allow ports to use them instead of hardcoding directory paths.

Do you think that would be a good approach?

[pwilkin]

You forgot to include the patch for the actual ports file:

include(vcpkg_common_functions)

if(NOT VCPKG_CMAKE_SYSTEM_NAME OR VCPKG_CMAKE_SYSTEM_NAME STREQUAL "WindowsStore")
    vcpkg_get_program_files_32_bit(PROGRAM_FILES_32_BIT)
    vcpkg_get_windows_sdk(WINDOWS_SDK)
    vcpkg_get_windows_sdk_path(WINDOWS_SDK_PATH)

    if (WINDOWS_SDK MATCHES "10.")
        set(LIBGLFILEPATH  "${WINDOWS_SDK_PATH}\\Lib\\${WINDOWS_SDK}\\um\\${TRIPLET_SYSTEM_ARCH}\\OpenGL32.Lib")
        set(LIBGLUFILEPATH "${WINDOWS_SDK_PATH}\\Lib\\${WINDOWS_SDK}\\um\\${TRIPLET_SYSTEM_ARCH}\\GlU32.Lib")
        set(HEADERSPATH    "${WINDOWS_SDK_PATH}\\Include\\${WINDOWS_SDK}\\um")
    elseif(WINDOWS_SDK MATCHES "8.")
        set(LIBGLFILEPATH  "${WINDOWS_SDK_PATH}\\Lib\\winv6.3\\um\\${TRIPLET_SYSTEM_ARCH}\\OpenGL32.Lib")
        set(LIBGLUFILEPATH "${WINDOWS_SDK_PATH}\\Lib\\winv6.3\\um\\${TRIPLET_SYSTEM_ARCH}\\GlU32.Lib")
        set(HEADERSPATH    "${WINDOWS_SDK_PATH}\\Include\\um")

(...)

[BillyONeal]

We believe that ports should use the environment variable provided by vcvarsall, WindowsSdkDir, rather than creating a specific vcpkg function to provide that location. We will fix up ports hard coding such paths to use that environment variable directly.

Thanks for your contribution, and sorry for the delay :(