[spirv] Require source location in decorateSample.

tools/clang/include/clang/SPIRV/SpirvBuilder.h

@@ -533,7 +533,7 @@ public:
                              SourceLocation srcLoc = {});
 
   /// \brief Decorates the given target with sample
-  void decorateSample(SpirvInstruction *target, SourceLocation srcLoc = {});
+  void decorateSample(SpirvInstruction *target, SourceLocation srcLoc);
 
   /// \brief Decorates the given target with patch
   void decoratePatch(SpirvInstruction *target, SourceLocation srcLoc);