solvers: Resolve link error when SCS is disabled (RobotLocomotion#10131)

This amends 1c3cd94 to provide the
const-Solve method even when SCS is disabled.

solvers/no_scs.cc

@@ -11,6 +11,15 @@ namespace solvers {
 
 bool ScsSolver::is_available() { return false; }
 
+void ScsSolver::Solve(const MathematicalProgram&,
+                      const optional<Eigen::VectorXd>&,
+                      const optional<SolverOptions>&,
+                      MathematicalProgramResult*) const {
+  throw std::runtime_error(
+      "The SCS bindings were not compiled.  You'll need to use a different "
+      "solver.");
+}
+
 SolutionResult ScsSolver::Solve(MathematicalProgram&) const {
   throw std::runtime_error(
       "The SCS bindings were not compiled.  You'll need to use a different "