Add some plumbing for the Utf8proc and LZ4 dependencies on Windows.
This avoids receiving the following warnings when running gen-make.py:
Warning: Using undeclared dependency '$(SVN_UTF8PROC_LIBS)'. Warning: Using undeclared dependency '$(SVN_LZ4_LIBS)'.
For now, we only support using the bundled versions of these libraries on Windows, but this patch (minimally) integrates them into the build env.
* build/generator/gen_win_dependencies.py (SVNCommonLibrary.__init__): Add new 'internal' field. (GenDependenciesBase._find_lz4, GenDependenciesBase._find_utf8proc): New functions that parse versions of bundled libraries and add them as internal SVNCommonLibrary objects. (GenDependenciesBase.find_libraries): Call new functions.
* build/generator/gen_win.py (WinGeneratorBase.__init__): Separately print all internal libraries.