libgcc gcov_fork failure on AIX

[David Edelsohn]

Richi,

Your patch for PR gcov/49484 now causes a bootstrap failure on AIX:

/farm/dje/src/src/libgcc/libgcov.c: In function '__gcov_fork':
/farm/dje/src/src/libgcc/libgcov.c:1008:5: error: 'mx' undeclared
(first use in this function)
/farm/dje/src/src/libgcc/libgcov.c:1008:5: note: each undeclared
identifier is reported only once for each function it appears in
make: *** [_gcov_fork.o] Error 1

# 1000 "/farm/dje/src/src/libgcc/libgcov.c"
pid_t
__gcov_fork (void)
{
  pid_t pid;
  extern __gthread_mutex_t __gcov_flush_mx;
  __gcov_flush ();
  pid = fork ();
  if (pid == 0)
    (mx) (&__gcov_flush_mx);
  return pid;
}