Compilation error on MacOS and solution

[huayue21]

Compilation error:
src/main/c/jni/org_jpy_PyLib.c

I compiled on Mac and gcc standard c99 reports error. So I put a line of declaration of
void JPy_free(void* unused);
in the file src/main/c/jni/org_jpy_PyLib.c
and this results further error since the calling on line 333 is
JPy_free();
does not comply with the form of the declaration.
I then change it to
JPy_free(NULL);
and it works for me.

Not sure what happens on Windows 10 and other compilers.