draft: Compiling LFortran to WASM

An attempt towards #583

I also tried to replicate/recreate @certik 's steps from !1549 (closed).

I am currently stuck on executing ./build2.sh. The file linklibs.rsp is not being generated.

ubaid@ubaid-Lenovo-ideapad-330-15ARR:~/Desktop/My-Projects/GSoC/lfortran$ ./build2.sh 
+ make -j16 wasm_demo
[  3%] Built target lfortran_runtime_static
[ 66%] Built target asr
[ 96%] Built target lfortran_lib
[100%] Built target wasm_demo
+ cd src/bin
+ em++ -Wall -Wextra -fexceptions @CMakeFiles/wasm_demo.dir/objects1.rsp -o wasm_demo.html @CMakeFiles/wasm_demo.dir/linklibs.rsp -s 'EXPORTED_RUNTIME_METHODS=["ccall", "cwrap"]' --shell-file shell_minimal.html
em++: error: response file not found: CMakeFiles/wasm_demo.dir/linklibs.rsp