Don't export symbols from static MSVC .obj files. Suggested by Dmitry Bely <dmitry.bely@gmail.com> in <https://lists.gnu.org/archive/html/bug-gnu-libiconv/2023-08/msg00002.html>. * include/export.h: Add a copyright notice. Set LIBICONV_DLL_EXPORTED to empty on MSVC when DLL_EXPORT is not defined. * Makefile.devel (include/iconv.h.build.in): Filter out the second copyright notice. * configure.ac (DLL_VARIABLE): Test DLL_EXPORT, not _DLL. * lib/relocatable.h: From gnulib: (RELOCATABLE_DLL_EXPORTED): Don't use __declspec(dllexport) when creating static .obj files with MSVC. * libcharset/include/export.h: Add a copyright notice. Set LIBCHARSET_DLL_EXPORTED to empty on MSVC when DLL_EXPORT is not defined. * libcharset/Makefile.devel (include/libcharset.h.build.in, include/localcharset.h.build.in): Filter out the second copyright notice.