Everyone gets a namespace {}.

src/core/SkNx.h

Index: src/core/SkNx.h
diff --git a/src/core/SkNx.h b/src/core/SkNx.h
index af7194840a4f028c8bc9dca0c339349a4a79866a..0f5aa829dfc99a5c271897d2e6bc97c55904b663 100644
--- a/src/core/SkNx.h
+++ b/src/core/SkNx.h
@@ -17,6 +17,13 @@
 #include <math.h>
 #define REQUIRE(x) static_assert(x, #x)
 
+// 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 {
+
 // The default implementations just fall back on a pair of size N/2.
 
 // SkNb is a _very_ minimal class representing a vector of bools returned by comparison operators.
@@ -251,6 +258,7 @@ protected:
     T fVal;
 };
 
+}  // namespace
 
 // Generic syntax sugar that should work equally well for all implementations.
 template <typename T> T operator - (const T& l) { return T(0) - l; }