Compilation error on muleDec when using MinGW/MSYS2

Using MSYS2 and MinGW(64) may cause the compilation of src/muleDec.c, according to its Readme.txt, to fail with error

undefined reference to 'WinMain'

This can be solved by additionally specifying -municode on the gcc command-line, as suggested at

https://stackoverflow.com/questions/58324230/undefined-reference-to-winmain-when-trying-to-use-wwinmain-c-mingw#58336414