Provide a way to selectively enable assertions in release mode

- Throwing an assertion exception for proper stack unwinding, making
  sure destructors are called

- On in Debug mode, in Release, enable via:

      cmake -DCMAKE_BUILD_TYPE=Release -DENABLE_ASSERTIONS=ON

Current problem that I'm seeing is that some code is not catching
exceptions or worse silently swallowing them. Would like to check the
whole pipeline before merging this in.

include/util/assert.hpp

@@ -0,0 +1,20 @@
+#ifndef OSRM_ASSERT_HPP
+#define OSRM_ASSERT_HPP
+
+#include <boost/assert.hpp>
+
+#include <stdexcept>
+
+namespace osrm
+{
+namespace util
+{
+// Assertion type to be thrown for stack unwinding
+struct assertionError final : std::logic_error
+{
+    assertionError(const char *msg) : std::logic_error{msg} {}
+};
+}
+}
+
+#endif