Extern inline functions are handled incorrectly when `merge_inlines` is `false`

[karoliineh]

When merge_inlines is false, extern inline functions that are used several times produce one CFG with as many duplicate paths as there are usages. Here is an example to reproduce:

Details

// foo.h
extern __inline int ex()
{
  return 0;
}

// bar.c
#include "foo.h"

void main() {
    ex();
}

// baz.c
#include "foo.h"

void main() {
    ex();
}

Goblint conf:

{
  "files": ["bar.c", "baz.c"],
  "cil": {
    "merge": {
      "inlines": false
    }
  }
}

Without the extern, inline functions are handled fine: renaming the function with an added suffix and producing one separate CFG for each.