Document build issues and dependencies with latest emscripten

[emnh]

Dependencies on Ubuntu are emscripten dependencies and for vim libncurses-dev, libxt-dev and cproto. PS: It can be a bit hard to track down what is missing because make proto will just omit definitions that require more headers rather than fail, so compile will fail later with the missing definitions. You can run e.g.

cd src
gcc -E -DPROTO -DFEAT_SMALL -DFEAT_GUI_WEB ui.c

on the file in question to check for error messages regarding headers.

While running configure, there is a problem that emcc calls clang instead of gcc and then doesn't pick up ncurses system library which makes the configure fail, so before configure do:

cd $EM_DIR
mv emcc emcc.orig
ln -s emcc gcc

Then after configure finishes and before building:

cd $EM_DIR
mv emcc emcc.link
mv emcc.orig emcc

There may be a better way to do this using an environment variable, but I didn't find it.

[lunu-bounir]

@emnh can you please clone this repo and apply the changes. I've tried to follow your instruction to rebuild the project with the latest emscripten but the compiled version doesn't work!