Add test for void type in struct.

Mysteriously, I had written a test which put arrays of void inside a
struct, but had neglected to include the non-array case. It causes an
okay-not-great error (referring to void as an "opaque type").

Change-Id: Id20a9d3512d29aecea81d46877dce708b7b2f973
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/472450
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>

gn/sksl_tests.gni

@@ -13,7 +13,6 @@ sksl_error_tests = [
   "/sksl/errors/ArrayNegation.sksl",
   "/sksl/errors/ArrayOfInvalidSize.sksl",
   "/sksl/errors/ArrayOfVoid.sksl",
-  "/sksl/errors/ArrayOfVoidInStruct.sksl",
   "/sksl/errors/ArrayPlus.sksl",
   "/sksl/errors/ArrayReturnTypes.sksl",
   "/sksl/errors/ArraySplitDimensions.sksl",
@@ -221,6 +220,7 @@ sksl_error_tests = [
   "/sksl/errors/VectorInlinedIndexOutOfRange.sksl",
   "/sksl/errors/VectorSlice.sksl",
   "/sksl/errors/VertexEarlyReturn.vert",
+  "/sksl/errors/VoidInStruct.sksl",
   "/sksl/errors/VoidVariable.sksl",
   "/sksl/errors/WhileTypeMismatch.sksl",
 ]

resources/sksl/errors/ArrayOfVoidInStruct.sksl

@@ -1,7 +0,0 @@
-// Expect 3 errors
-
-struct S {
-    void a[2];
-    void[2] b;
-    void[2] c[2];
-};

resources/sksl/errors/VoidInStruct.sksl

@@ -0,0 +1,8 @@
+// Expect 4 errors
+
+struct S {
+    void a;
+    void b[2];
+    void[2] c;
+    void[2] d[2];
+};

tests/sksl/errors/VoidInStruct.glsl

@@ -1,6 +1,7 @@
 ### Compilation failed:
 
-error: 4: type 'void' may not be used in an array
 error: 5: type 'void' may not be used in an array
 error: 6: type 'void' may not be used in an array
-3 errors
+error: 7: type 'void' may not be used in an array
+error: 4: opaque type 'void' is not permitted in a struct
+4 errors