Merge topic 'vs-instance'

46e9ff5729 Restore honoring CMAKE_GENERATOR_INSTANCE in toolchain file
42418b02f7 Android: Refactor sysroot detection under Visual Studio
44a86d0b38 cmake_host_system_information: Add undocumented VS_MSBUILD_COMMAND key
6999b87133 cmGlobalVisualStudio10Generator: Add method to find MSBuild early
7f730464be cmGlobalGenerator: Add method to check if generator is at least VS 10
8917b8512f cmGlobalVisualStudioVersionedGenerator: Allow repeating SetGeneratorInstance
6511654164 cmGlobalVisualStudio10Generator: Allow subclasses to reset MSBuild search

Acked-by: Kitware Robot <kwrobot@kitware.com>
Tested-by: buildbot <buildbot@kitware.com>
Merge-request: !6646