GSdx: Re-add __forceinline to GSVector functions

Looks like MSVC isn't smart enough to inline things properly

plugins/GSdx/GSVector4.h

@@ -135,7 +135,7 @@ public:
 		m = _mm_cvtepi32_ps(_mm_loadl_epi64((__m128i*)&v));
 	}
 
-	constexpr explicit GSVector4(__m128 m)
+	__forceinline constexpr explicit GSVector4(__m128 m)
 		: m(m)
 	{
 	}

plugins/GSdx/GSVector4i.h

@@ -70,7 +70,7 @@ public:
 		__m128i m;
 	};
 
-	constexpr GSVector4i(): x(0), y(0), z(0), w(0)
+	__forceinline constexpr GSVector4i(): x(0), y(0), z(0), w(0)
 	{
 	}
 
@@ -129,7 +129,7 @@ public:
 		*this = i;
 	}
 
-	constexpr explicit GSVector4i(__m128i m)
+	__forceinline constexpr explicit GSVector4i(__m128i m)
 		: m(m)
 	{
 	}

plugins/GSdx/GSVector8.h

@@ -164,7 +164,7 @@ public:
 		*this = m;
 	}
 
-	constexpr explicit GSVector8(__m256 m)
+	__forceinline constexpr explicit GSVector8(__m256 m)
 		: m(m)
 	{
 	}

plugins/GSdx/GSVector8i.h

@@ -154,7 +154,7 @@ public:
 		*this = m;
 	}
 
-	constexpr explicit GSVector8i(__m256i m)
+	__forceinline constexpr explicit GSVector8i(__m256i m)
 		: m(m)
 	{
 	}