base: build as a DLL, one Option/Feature registry on Windows

[Force67]

For rx's Windows component build (every module a DLL).

• EQ_BASE_SHARED builds base as a shared library. PE gives every DLL that links a static library its own copy of its globals, so base has to be one DLL for one log, allocator and registry. Exports all functions (MSVC: WINDOWS_EXPORT_ALL_SYMBOLS; mingw: --export-all-symbols with the static runtime excluded).
• The Option/Feature chain roots move out of line on Windows (Feature::ChainRoot, OptionBase::ChainRoot in containers/init_chain_win.cc). A function-local static in an inline template is per DLL on PE whatever base is built as. ELF keeps the default-visibility inline root from base: one Option/Feature registry per process in shared-object builds #26.
• minwin.h on mingw undefines GetProp/SetProp/RemoveProp/MemoryBarrier after <windows.h>, matching the MSVC path, which never includes it. They renamed methods in the files that saw the header and not in others, and links failed.
• Remove debugging_win.cc: debugging.cc already defines IsDebuggerAttached for Windows, and a DLL link reports the duplicate a static archive hid.

Verified: base unit tests; rx Linux static and shared ctest 155/155; rx Windows static and DLL builds under Wine agree (renders rmse <= 0.0007, an option set from the environment reaches the render DLL).