fix: simplify include path assignment

[danielinux]

Both musl and gnu build can use the musl system path to resolve libc symbols/includes.

This fix removes dependencies on relative paths, so now cjit can run from anywhere.

Target make install added

[jaromil]

This still requires musl to be installed everywhere... I am trying another more portable solution.

[danielinux]

This still requires musl to be installed everywhere... I am trying another more portable solution.

This was already the case for the static musl build, I think it's OK to depend on musl if required on linux-x86. I can move this to gnu libc via /usr/include if it sounds better and reduces dependencies for linux-x86. Eventually linux-x86 uses GNU libc, so it makes sense to import the original glibc includes there.

[danielinux]

Last commit (968ec9f) ensures that the LIBC_MUSL build only uses musl symbols and does not import any GNU LIBC from the compiling host. This is done via -nostdlib flags, so the cjit binary is correctly linked to musl libc functions only.

[jaromil]

OK, this is definitely an improvement! cheers