Add support to produce WebAssembly runtime assets (dotnet/corefx#42128)

Add support to produce WebAssembly runtime assets (dotnet/corefx#42128)

* Add support to produce WebAssembly runtime assets

* Add support to build in OSX and address PR feedback

* Change AND -> and in Directory.Build.props change region

* PR Feedback: run build in rolling CI builds as well

* Add TODO comment for WebAssembly OSGroup

* Fix indentation.

* Fix wrong #include as apis defined in that include are used outside of ETHTOOL_H #if-def

Commit migrated from https://github.com/dotnet/corefx/commit/179013357896ab947523bdf9961c02f8504db6ff