ABI compliance with multi-register NEON intrinsics

When using NEON intrinsics that use two or more registers and the hard float calling convention, GCC puts the argument in core registers instead of NEON registers.

For example, this test:

#include <arm_neon.h>

void foo(uint32x4x2_t v);

void bar()
{
  uint32x4x2_t v = { 0, };

  foo(v);
}

calls foo with v in r0-r3 and the stack. v should be in q0-q1.

This is rare as it applies to hard float NEON installations where multi-register NEON intrinsics are passed across an API.