Add extra break statements to quiet clang warnings.

Clang complains about code that falls through into an empty default
case, so add some breaks to placate it.

glslang/MachineIndependent/ParseContextBase.cpp

@@ -257,6 +257,7 @@ void TParseContextBase::rValueErrorCheck(const TSourceLoc& loc, const char* op,
             case EOpVectorSwizzle:
             case EOpMatrixSwizzle:
                 rValueErrorCheck(loc, op, binaryNode->getLeft());
+                break;
             default:
                 break;
             }