buildsystem: fix typo

    modified:   Makefile.common
buildsystem: fix that library_auto.def is appended when updated

It should be recreated.

    modified:   Makefile.common
buildsystem: do not export _DLL_InitTerm

    modified:   Makefile.common
buildsystem: support __declspec(dllexport)

__declspec(dllexport) does not require .def. If .def is used and it
has symbols declared with __declspec(dllexport), a linker complains
that they are 'already exported'.

In addition, symbols declared with __declspec(dllexport) should be
imported from DLLs directly.

    modified:   Makefile
    modified:   Makefile.common
buildsystem: add comments to mark a part of programs and libraries

    modified:   Makefile