* src/w32-add.h (gpgrt_w32_iconv_t): New.
(gpgrt_w32_iconv_open, gpgrt_w32_iconv_close, gpgrt_w32_iconv): New.
( GPGRT_ENABLE_W32_ICONV_MACROS): New
* src/w32-iconv.c: Change license to LGPLv2.1+.  Dispable mlang
feature.  Remove external DLL loading.  Simplify iconv functions.  Use
cleaner context struct pattern.  Use gpgrt namespace.
* src/gpg-error.def.in: Add new functions.