Update EXTRA_DIST in Makefile, Win32/64 docs after NT_*_MAKEFILE removal

Update EXTRA_DIST in Makefile, Win32/64 docs after NT_*_MAKEFILE removal
(fix commit 8312098)

* Makefile.am (EXTRA_DIST): Remove NT_STATIC_THREADS_MAKEFILE,
NT_X64_STATIC_THREADS_MAKEFILE, NT_X64_THREADS_MAKEFILE.
* Makefile.direct (OTHER_MAKEFILES): Likewise.
* doc/README.win32 (Threads): Do not refer to NT_THREADS_MAKEFILE;
replace NT_STATIC_THREADS_MAKEFILE to NT_MAKEFILE.
* doc/README.win64: Replace NT_X64_STATIC_THREADS_MAKEFILE and
NT_X64_THREADS_MAKEFILE to NT_MAKEFILE; update documentation
accordingly; update note about Test_cpp failures; update note about
suppressed warnings.