GCC ignores all five of the attributes in the test case below but only diagnoses one of them, on the declaration of f_ref_noreturn.  It should diagnose all of them.

$ cat t.C && gcc -S -Wall -Wextra -Wpedantic -Wignored-attributes t.C
void f_ptr_unused (void * __attribute__((unused)));

void f_ptr_unused (void *p)   // -Wunused issued regardless of attribute
{
}

int f_ptr_noreturn (void (*)() __attribute__((noreturn)));

int f_ptr_noreturn (void (*fp)())
{
  fp ();   // -Wreturn-type regardless of attribute
}


int f_ref_noreturn (void (&)() __attribute__((noreturn)));   // warning (ok)

int f_ptr_noreturn (void (&fr)())
{
  fr ();   // -Wreturn-type (expected, warning on declaration)
}


template <void (*FP)() __attribute__((noreturn))>
int ftempl_ptr_noreturn ()
{
  FP ();   // -Wreturn-type regardless of attribute
}

void f ();

template int ftempl_ptr_noreturn<&f>();

template <void (&FR)() __attribute__((noreturn))>
int ftempl_ref_noreturn ()
{
  FR ();   // -Wreturn-type regardless of attribute
}

template int ftempl_ref_noreturn<f>();

t.C: In function ‘void f_ptr_unused(void*)’:
t.C:3:26: warning: unused parameter ‘p’ [-Wunused-parameter]
 void f_ptr_unused (void *p)   // -Wunused issued regardless of attribute
                          ^
t.C: In function ‘int f_ptr_noreturn(void (*)())’:
t.C:12:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^
t.C: At global scope:
t.C:15:56: warning: ‘noreturn’ attribute ignored [-Wattributes]
 int f_ref_noreturn (void (&)() __attribute__((noreturn)));   // warning (ok)
                                                        ^
t.C: In function ‘int f_ptr_noreturn(void (&)())’:
t.C:20:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^
t.C: In function ‘int ftempl_ptr_noreturn()’:
t.C:27:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^
t.C: In function ‘int ftempl_ref_noreturn()’:
t.C:37:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^