Adds support for str type to ccall

[dylon]

No description provided.

[dylon]

File: main.py

from ltypes import ccall

@ccall
def prn(msg: str) -> None:
    pass

prn("Hello World!")

File: main.c

#include <stdio.h>

void prn(char * msg) {
  printf("%s\n", msg);
}

Compile library:

clang -shared -o libprn.so main.c

Execute:

PYTHONPATH=~/Workspace/lpython/src/runtime/ltypes LPYTHON_PY_MOD_NAME=prn LPYTHON_PY_MOD_PATH=. python main.py

Output:

Hello World!

[czgdp1807]

Looks good. Can we add a test as well?

[czgdp1807]

Let's copy chagnes in test_c_interop_02 from https://github.com/lcompilers/lpython/pull/671/files and apply here.

[czgdp1807]

@dylon Will you mind if I do this? LLVM backend works fine. C backend needs some minor changes to get it working. Please let me know if you are okay with me pushing changes to your branch. Thanks.

[certik]

I am working on tests right now, almost done.

[certik]

This is ready.