[CM] s7 wrap c func with scheme

[bil at ccrma.Stanford.EDU]

I just conjured up this example (9/10 of the time
was spent fussing with the compiler flags...):

file add1.c:

#include <stdlib.h>
#include "s7.h"

static s7_pointer add1(s7_scheme *sc, s7_pointer args)
{
   if (s7_is_integer(s7_car(args)))
     return(s7_make_integer(sc, 1 + s7_integer(s7_car(args))));
   return(s7_wrong_type_arg_error(sc, "add1", 1, s7_car(args), "an 
integer"));
}

void add1_init(s7_scheme *sc);
void add1_init(s7_scheme *sc)
{
   s7_define_function(sc, "add1", add1, 1, 0, false, "(add1 int) adds 1 
to int");
}

now build it as a shared object, build s7 with -fpic,
and load add1 into s7 at runtime:

gcc -fpic -c add1.c
gcc -shared -Wl,-soname,libadd1.so -o libadd1.so add1.o -lm -lc
gcc s7.c -o repl -fpic -DWITH_MAIN -I. -ldl -lm -Wl,-export-dynamic 
-DUSE_SND=0
repl
   > (load "libadd1.so" (inlet 'init_func 'add1_init))
   > (add1 2)