Fix the compilation error for turbofan unsupported platform.

  Fix the compilation error for turbofan unsupported platform. The Linkage::GetOsrValuePosition()
  function is implemented in linkage-impl.h. And this file is included by different platform specific
  file separately. This leads to compilation error for turbofan unsupported platform.

  The fix is adding one dummy implementation in linkage.cc.

BUG=

Review URL: https://codereview.chromium.org/848873002

Cr-Commit-Position: refs/heads/master@{#26041}

src/compiler/linkage.cc

@@ -232,6 +232,12 @@ CallDescriptor* Linkage::GetJSCallDescriptor(int parameter_count, Zone* zone,
 }
 
 
+LinkageLocation Linkage::GetOsrValueLocation(int index) const {
+  UNIMPLEMENTED();
+  return LinkageLocation(-1);  // Dummy value
+}
+
+
 CallDescriptor* Linkage::GetRuntimeCallDescriptor(
     Runtime::FunctionId function, int parameter_count,
     Operator::Properties properties, Zone* zone) {