HLSL: Improve setting and testing of interpolation qualifiers.

Notably, use of 'linear' on a non-input could mark it as an input.

Test/hlsl.struct.frag

@@ -16,7 +16,7 @@ struct {
     float4 i;
 } s2;
 
-struct {
+struct IN_S {
     linear float4 a;
     nointerpolation bool b;
     noperspective centroid float1 c;
@@ -25,19 +25,19 @@ struct {
     bool ff2 : packoffset(c0.y);
     bool ff3 : packoffset(c0.y) : register(ps_5_0, s0) ;
     float4 ff4 : VPOS : packoffset(c0.y) : register(ps_5_0, s0) <int bambam=30;> ;
-} s4;
+};
 
 float3 ff5 : packoffset(c1.y) : register(ps_5_0, s[5]);
 float3 ff6 : packoffset(c2.y) : register(s3[5]);
 
-float4 PixelShaderFunction(float4 input) : COLOR0
+float4 PixelShaderFunction(float4 input, IN_S s) : COLOR0
 {
     struct FS {
         bool3 b3;
     } s3;
 
     s3 == s3;
-    s2.i = s4.ff4;
+    s2.i = s.ff4;
 
     return input;
 }