Everyone gets a namespace {}.

src/core/Sk4px.h

Index: src/core/Sk4px.h
diff --git a/src/core/Sk4px.h b/src/core/Sk4px.h
index 48e09e1c9200d3dbb2d87f4441ca2f534a037cae..8fb546a40639f851abc6192a954d5df21c5a1f03 100644
--- a/src/core/Sk4px.h
+++ b/src/core/Sk4px.h
@@ -11,6 +11,13 @@
 #include "SkNx.h"
 #include "SkColor.h"
 
+// This file may be included multiple times by .cpp files with different flags, leading
+// to different definitions.  Usually that doesn't matter because it's all inlined, but
+// in Debug modes the compilers may not inline everything.  So wrap everything in an
+// anonymous namespace to give each includer their own silo of this code (or the linker
+// will probably pick one randomly for us, which is rarely correct).
+namespace {
+
 // 1, 2 or 4 SkPMColors, generally vectorized.
 class Sk4px : public Sk16b {
 public:
@@ -171,6 +178,8 @@ private:
     typedef Sk16b INHERITED;
 };
 
+}  // namespace
+
 #ifdef SKNX_NO_SIMD
     #include "../opts/Sk4px_none.h"
 #else