[Gretl-devel] Building gretl on Windows: add libdl

For anyone building gretl on MS Windows: I've added an MSYS2 dependency, namely mingw-w64-x86_64-dlfcn (or mingw-w64-i686-dlfcn for a 32-bit build). This contains libdl.dll -- a small library that adds POSIX functionality for loading and querying modules, which is useful for libgretl in figuring out what blas/lapack variant we're looking at. The files pkglist.txt and pkglist32.txt at http://ricardo.ecn.wfu.edu/pub/gretl/winbuild/ are updated accordingly. Allin