Add metacall include path and metacall library path in c loader

[rxbryan]

Description

Add metacall include path so including metacall/metacall.h #include <metacall/metacall.h> works.
Add metacall library path so libtcc can find libmetacall.so.

Fixes #(issue_no)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Documentation update

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• I have made corresponding changes to the documentation.
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[viferga]

I am not sure if this is going to work as it is for all cases. It is making me doubt, so I am not sure to merge it. I can try to implement a sightly better version and link it here.

[rxbryan]

I can try to implement a sightly better version and link it here.

ok, looking forward to it

[viferga]

I think we can implement this with portability/path module, so it works for multiple platforms and it handles all the cases (i.e if the path ends with or without slash). Meanwhile I don't want to merge it, but we can leave it for reference.

We can also use filesystem module from c++ 17 but I don't like it, it's very heavy. The portability path are just few small C functions with size safety. We can just use portability_path_join.

[rxbryan]

We can also use filesystem module from c++ 17 but I don't like it, it's very heavy. The portability path are just few small C functions with size safety. We can just use portability_path_join.
Ok. should I rework the code and update the pr?

[viferga]

We can also use filesystem module from c++ 17 but I don't like it, it's very heavy. The portability path are just few small C functions with size safety. We can just use portability_path_join.
Ok. should I rework the code and update the pr?

Yeah, feel free to do it.