Why can I goto into the scope of a alloca:d variable, but not a variable length array?

See this test program:

#include <stdio.h>
#include <string.h>

int main(int argc, char *argv[])
{
  if (argc < 2)
    goto end;

  char s[strlen(argv[1]) + 1];
  strcpy(s, argv[1]);
  printf("s=%s\n", s);

end:
  return 0;
}

It fails to compile with the error "jump into scope of identifier with variably modified type" (see other question).

However it compiles fine if I change the declaration of s into this (and include alloca.h):

char *s = alloca(strlen(argv[1]) + 1);

Why does the C standard allow jumping into the scope of an object created with alloca, but not a variable length array? I thought they were equivalent.