GS: Make vector types POD

Generates the same code in Release, but slightly difference code in Debug.
In Debug, with the default copy assignment operator, it turns into two
8-byte moves. With the overloaded operator, it turns into a function call
with a vector move.

pcsx2/GS/GSVector4.h

@@ -55,8 +55,6 @@ public:
 
 	GSVector4() = default;
 
-	constexpr GSVector4(const GSVector4&) = default;
-
 	constexpr static GSVector4 cxpr(float x, float y, float z, float w)
 	{
 		return GSVector4(cxpr_init, x, y, z, w);
@@ -177,11 +175,6 @@ public:
 		return GSVector4(_mm_castpd_ps(_mm_set_pd(y, x)));
 	}
 
-	__forceinline void operator=(const GSVector4& v)
-	{
-		m = v.m;
-	}
-
 	__forceinline void operator=(float f)
 	{
 #if _M_SSE >= 0x501

pcsx2/GS/GSVector4i.h

@@ -43,10 +43,7 @@ public:
 		__m128i m;
 	};
 
-	__forceinline constexpr GSVector4i()
-		: x(0), y(0), z(0), w(0)
-	{
-	}
+	GSVector4i() = default;
 
 	constexpr static GSVector4i cxpr(int x, int y, int z, int w)
 	{
@@ -88,11 +85,6 @@ public:
 	{
 	}
 
-	__forceinline GSVector4i(const GSVector4i& v)
-	{
-		m = v.m;
-	}
-
 	__forceinline explicit GSVector4i(const GSVector2i& v)
 	{
 		m = _mm_loadl_epi64((__m128i*)&v);
@@ -125,11 +117,6 @@ public:
 
 #endif
 
-	__forceinline void operator=(const GSVector4i& v)
-	{
-		m = v.m;
-	}
-
 	__forceinline void operator=(int i)
 	{
 #if _M_SSE >= 0x501

pcsx2/GS/GSVector8.h

@@ -115,8 +115,6 @@ public:
 #endif
 	}
 
-	constexpr GSVector8(const GSVector8& v) = default;
-
 	__forceinline explicit GSVector8(float f)
 	{
 		*this = f;
@@ -163,11 +161,6 @@ public:
 	__forceinline static GSVector8 cast(const GSVector4& v);
 	__forceinline static GSVector8 cast(const GSVector4i& v);
 
-	__forceinline void operator=(const GSVector8& v)
-	{
-		m = v.m;
-	}
-
 	__forceinline void operator=(float f)
 	{
 #if _M_SSE >= 0x501

pcsx2/GS/GSVector8i.h

@@ -90,8 +90,6 @@ public:
 #endif
 	}
 
-	GSVector8i(const GSVector8i& v) = default;
-
 	__forceinline explicit GSVector8i(int i)
 	{
 		*this = i;
@@ -107,11 +105,6 @@ public:
 	{
 	}
 
-	__forceinline void operator=(const GSVector8i& v)
-	{
-		m = v.m;
-	}
-
 	__forceinline void operator=(int i)
 	{
 		m = _mm256_broadcastd_epi32(_mm_cvtsi32_si128(i)); // m = _mm256_set1_epi32(i);