a.pas

program a;

{$L ac.o}
{$LinkLib c}
{$LinkLib gcc_s}

procedure install_foo;cdecl;external;

begin
install_foo;
end.

ac.c

#include <stdlib.h>
#include <stdio.h>

void __attribute__ ((destructor)) stuff3() {
  printf("baz\n");
}

void __attribute__ ((constructor)) stuff2() {
  printf("bar\n");
}

void stuff() {
  printf("foo\n");
}

void install_foo() {
  atexit(&stuff);
}

b.pas

program a;

{$L bc.o}
{$LinkLib c}
{$LinkLib stdc++}
{$LinkLib gcc_s}

uses initc;

begin
end.

bc.cpp

#include <cstdio>

bool do_foo() {
	printf("foo\n");
	return true;
}

static bool foo = do_foo();

output

gcc -c ac.c
fpc a.pas
Free Pascal Compiler version 2.6.4 [2014/03/12] for x86_64
Copyright (c) 1993-2014 by Florian Klaempfl and others
Target OS: Linux for x86-64
Compiling a.pas
Linking a
/usr/bin/ld: warning: link.res contains output sections; did you forget -T?
11 lines compiled, 0.1 sec 
./a
foo
baz

g++ -c bc.cpp
fpc b.pas
Free Pascal Compiler version 2.6.4 [2014/03/12] for x86_64
Copyright (c) 1993-2014 by Florian Klaempfl and others
Target OS: Linux for x86-64
Compiling b.pas
Linking b
/usr/bin/ld: warning: link.res contains output sections; did you forget -T?
11 lines compiled, 0.1 sec 
./b

run

#!/bin/bash

set -e
set -v

gcc -c ac.c
fpc a.pas
./a

g++ -c bc.cpp
fpc b.pas
./b