Block-scope ordinary identifiers with variably modified type are required
to have no linkage.  Block-scope function declarations implicitly have
external linkage.  However, GCC diagnoses such declarations with variably
modified type only with an explicit "extern".

The code

int a;
void
f (void)
{
  typedef int T[a];
  extern T *g (void);
}

is correctly diagnosed with -std=c99 -pedantic-errors, although the error
message "object with variably modified type must have no linkage" is
bad (it's a function, not an object).  The equivalent code

int a;
void
f (void)
{
  typedef int T[a];
  T *g (void);
}

should be diagnosed, but is not.