libc_hidden_proto

libc_hidden_proto causes the symbol to lose its special attributes,
e.g. if it had __attribute__((noreturn)).  For noreturn this meanings
spurious warnings in libc code, but for const it could hurt optimization
and for any weirder ones (regparm!) it could really be a problem.

I cannot reproduce this for const or regparm.  These are the two I tried.

extern int foo (int) __attribute ((regparm (1), const));
//extern int bar (int) __attribute ((regparm (1), const));
__typeof (foo) __foo;
__typeof (foo) foo __asm ("__foo") __attribute ((visibility ("hidden")));
int
foo (int a)
{
  return a;
}
int
bar (int a)
{
  return a;
}
int
xyzzy (int a)
{
  return foo (a) == 1 || foo (a) == 2;
}
int
xyzzy2 (int a)
{
  return bar (a) == 1 || bar (a) == 2;
}