AC_CHECK_FUNC not safe WRT link time optimizing compilers

[Jan Hubicka]

Hi,
AC_CHECK_FUNC produce test like the following:
char pstat_getstatic ();
char (*f) () = pstat_getstatic;
int
main ()
{
  return f != pstat_getstatic;
}


New GCC with link time optimization is smart enough to ask the linker plugin 
and work out that
variable F is used only by the LTO code.  This makes GCC to promote F as read 
only variable
since it is never written and the test to be optimized away.

Would be possible to fix this, for example, by converting it to:
int pstat_getstatic ();
int
main ()
{
  return pstat_getstatic ();
}

or by marking F volatile?
See http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46055
this prevents me from making GCC to use linker plugin information correctly.

Honza