Use a python script to generate the list of sources to build.
Now we don't include moc_*.cpp files in build by default, instead
we list only non-empty ones.
If you change a header so that the corresponding moc_*.cpp changes
its emptyness you may need to gyp/refresh to apply this change.
This should speed up the build significantly on GCC.
MetaLang, codegen_style and codegen_numbers utilities are now
built by GYP targets, rules added for codegen_style and actions
added for codegen_numbers and MetaLang.
WinXP supported without Windows 7.1A SDK, but with explicitly
setting MinimumRequiredVersion=5.01. It works (and that is strange).
If you attempt to use MSBuild instead of Ninja you should add
the latest Windows SDK include paths to include_dirs, because v140_xp
toolset implies the Windows 7.1A SDK (and is ignored by Ninja).
John Preston