Implement unbound varibility for struct types.

Now, if a struct member has an explicit 'uniform' or 'varying'
qualifier, then that member has that variability, regardless of
the variability of the struct's variability.  Members without
'uniform' or 'varying' have unbound variability, and in turn
inherit the variability of the struct.

As a result of this, now structs can properly be 'varying' by default,
just like all the other types, while still having sensible semantics.

examples/deferred/kernels.ispc

@@ -35,35 +35,35 @@
 
 struct InputDataArrays
 {
-    uniform float * uniform zBuffer;
-    uniform unsigned int16 * uniform normalEncoded_x; // half float
-    uniform unsigned int16 * uniform normalEncoded_y; // half float
-    uniform unsigned int16 * uniform specularAmount; // half float
-    uniform unsigned int16 * uniform specularPower; // half float
-    uniform unsigned int8 * uniform albedo_x; // unorm8
-    uniform unsigned int8 * uniform albedo_y; // unorm8
-    uniform unsigned int8 * uniform albedo_z; // unorm8
-    uniform float * uniform lightPositionView_x;
-    uniform float * uniform lightPositionView_y;
-    uniform float * uniform lightPositionView_z;
-    uniform float * uniform lightAttenuationBegin;
-    uniform float * uniform lightColor_x;
-    uniform float * uniform lightColor_y;
-    uniform float * uniform lightColor_z;
-    uniform float * uniform lightAttenuationEnd;
+    uniform float *zBuffer;
+    uniform unsigned int16 *normalEncoded_x; // half float
+    uniform unsigned int16 *normalEncoded_y; // half float
+    uniform unsigned int16 *specularAmount; // half float
+    uniform unsigned int16 *specularPower; // half float
+    uniform unsigned int8 *albedo_x; // unorm8
+    uniform unsigned int8 *albedo_y; // unorm8
+    uniform unsigned int8 *albedo_z; // unorm8
+    uniform float *lightPositionView_x;
+    uniform float *lightPositionView_y;
+    uniform float *lightPositionView_z;
+    uniform float *lightAttenuationBegin;
+    uniform float *lightColor_x;
+    uniform float *lightColor_y;
+    uniform float *lightColor_z;
+    uniform float *lightAttenuationEnd;
 };
 
 struct InputHeader
 {
-    uniform float cameraProj[4][4];
-    uniform float cameraNear;
-    uniform float cameraFar;
+    float cameraProj[4][4];
+    float cameraNear;
+    float cameraFar;
 
-    uniform int32 framebufferWidth;
-    uniform int32 framebufferHeight;
-    uniform int32 numLights;
-    uniform int32 inputDataChunkSize;
-    uniform int32 inputDataArrayOffsets[idaNum];
+    int32 framebufferWidth;
+    int32 framebufferHeight;
+    int32 numLights;
+    int32 inputDataChunkSize;
+    int32 inputDataArrayOffsets[idaNum];
 };
 
 
@@ -575,8 +575,6 @@ SplitTileMinMax(
     uniform float light_positionView_z_array[],
     uniform float light_attenuationEnd_array[],
     // Outputs
-    // TODO: ISPC doesn't currently like multidimensionsal arrays so we'll do the
-    // indexing math ourselves
     uniform int32 subtileIndices[],
     uniform int32 subtileIndicesPitch,
     uniform int32 subtileNumLights[]