[vcpkg] Add option cmake-args

[Neumann-A]

to pass additional args to the cmake script execution within vcpkg

things users/maintainers might want to pass:
--trace/--trace-expand
CMAKE_MESSAGE_LOG_LEVEL
CMAKE_MESSAGE_INDENT
CMAKE_MESSAGE_CONTEXT_SHOW/ --log-context (If vcpkg would use CMAKE_MESSAGE_CONTEXT)
PORT_DEBUG=ON

[LilyWangL]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[ras0219]

This should probably imply/require --editable.

[Neumann-A]

@ras0219 This is not passed to the vcpkg_configure_cmake.
This is added to [DEBUG] CreateProcessW("E:\vcpkg_cache\downloads\tools\cmake-3.17.2-windows\cmake-3.17.2-win32-x86\bin\cmake.exe" <alot of cmake_args> -P "E:\qt_zstd\scripts\ports.cmake")

[ras0219]

Sure, but the point is that these options can change the behavior of the package build -- that means they shouldn't be used as a basis for a cached binary tree.

[Neumann-A]

Then there needs to be a whitelist for cmake-args which don't imply --editable. (Mainly those vars mentioned in the very first comment.)

[strega-nil]

We had a discussion about this at today's meeting, and our opinion is that:

1. The option needs to be renamed --x-cmake-args
2. This needs to imply --editable for now, and we can special case stuff afterwards.

Once those are in, we're up to merge.

[Neumann-A]

@strega-nil Done

[strega-nil]

Thanks @Neumann-A