MINGW compilation instructions (under cygwin)

1/ install mingw 32 bits
2/ set path in path.mingw and configure.mingw according to your installation
3/ source path.mingw
4/ copy config.h.mingw to config.h and src/config.h
5/ cd src
6/ copy Makefile.mingw to Makefile
7/ run make giac.dll or make icas