Teuchos: remove compiler warning by adding a return

Build/Test Cases Summary
Enabled Packages: TeuchosCore, TpetraCore
Disabled Packages: PyTrilinos,Claps,TriKota
Enabled all Forward Packages
0) MPI_RELEASE_DEBUG_SHARED_PT => passed: passed=2435,notpassed=0 (493.16 min)
Other local commits for this build/test group: 90bca49

packages/teuchos/core/src/Teuchos_RCPNode.hpp

@@ -132,6 +132,7 @@ class TEUCHOSCORE_LIB_DLL_EXPORT ToStringTraits<ERCPStrength> {
       // Should never get here!
 #ifdef TEUCHOS_DEBUG
       TEUCHOS_TEST_FOR_EXCEPT(true);
+      return "";
 #else
       return "";
 #endif