HLSL: Do structure conversion for return type struct-punning on non-entry-point functions.

Test/baseResults/remap.hlsl.templatetypes.everything.frag.out

@@ -5,7 +5,7 @@ Linked fragment stage:
 
 // Module Version 10000
 // Generated by (magic number): 80001
-// Id's are bound by 16123
+// Id's are bound by 9012
 
                               Capability Shader
                               Capability Float64
@@ -20,11 +20,12 @@ Linked fragment stage:
               13:             TypeFloat 32
               29:             TypeVector 13(float) 4
             2572:   13(float) Constant 0
-             666:             TypePointer Output 29(fvec4)
-            4045:    666(ptr) Variable Output
-             667:             TypePointer Input 29(fvec4)
-            4872:    667(ptr) Variable Input
+             650:             TypePointer Output 13(float)
+            4045:    650(ptr) Variable Output
+             666:             TypePointer Input 29(fvec4)
+            4872:    666(ptr) Variable Input
             5663:           8 Function None 1282
-           16122:             Label
-                              ReturnValue 2572
+            9011:             Label
+                              Store 4045 2572
+                              Return
                               FunctionEnd