replace std::aligned_union

Since we're only describing the type size and alignment,
we can just use ordinary unions here.

This fixes the size and alignment of AllVertexData,
I think.

Bug: skia:10921
Change-Id: Ife5c1a1f52caf463d28a78b1f35d78e0bbeaeddc
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/333478
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>

Author: Mike Klein

src/gpu/text/GrTextBlob.cpp

@@ -1336,16 +1336,19 @@ GrTextBlob::~GrTextBlob() = default;
 
 sk_sp<GrTextBlob> GrTextBlob::Make(const SkGlyphRunList& glyphRunList, const SkMatrix& drawMatrix) {
     // The difference in alignment from the storage of VertexData to SubRun;
-    using AllSubRuns = std::aligned_union_t<1,
-            DirectMaskSubRun,
-            TransformedMaskSubRun,
-            SDFTSubRun,
-            PathSubRun>;
-
-    using AllVertexData = std::aligned_union<1,
-            DirectMaskSubRun::VertexData,
-            TransformedMaskSubRun::VertexData,
-            SDFTSubRun::VertexData>;
+    union AllSubRuns {
+        ~AllSubRuns() = delete;  // MSVC warns this is implicit if we don't write it explicitly.
+        DirectMaskSubRun      d;
+        TransformedMaskSubRun t;
+        SDFTSubRun            s;
+        PathSubRun            p;
+    };
+    union AllVertexData {
+        DirectMaskSubRun     ::VertexData d;
+        TransformedMaskSubRun::VertexData t;
+        SDFTSubRun           ::VertexData s;
+    };
+
     constexpr size_t alignDiff = alignof(AllSubRuns) - alignof(AllVertexData);
     constexpr size_t vertexDataToSubRunPadding = alignDiff > 0 ? alignDiff : 0;
     size_t totalGlyphCount = glyphRunList.totalGlyphCount();