yosys-config paths are wrong / windows support

[Ed Bordin]

Specifically we probably want to support yosys-config --bindir and yosys-config --datdir.
E.g. seems to be a common use-case to point sim tools to cell libs: yosys-config --datdir/ice40/cells_sim.v

It would be safest if the other options --cxx, --cxxflags, --ldflags, --ldlibs throw an error so it is clear they are unsupported. The supported options should output absolute paths generated relative to the script's location. Probably easiest to just ship our own version of the script rather than patching.

Also consider getting it to work on windows in e.g. git bash.

[Ed Bordin]

Draft: https://gist.github.com/edbordin/b4872462dfe2f249ecb3730239e11906

[Ed Bordin]

added custom script - should work under a bash shell in windows, tools needing windows paths will need to use something like cygpath to convert the path