Simplify backtrace output

This makes backtrace readable

src/language/ast/ASTBacktrace.cpp

@@ -26,6 +26,15 @@ ASTBacktrace::errorMessageAt(const std::string& message) const
   return error_msg.str();
 }
 
+SourceLocation
+ASTBacktrace::sourceLocation() const
+{
+  auto& stack = ASTBacktrace::getInstance().m_stack;
+
+  auto p = stack[stack.size() - 1]->begin();
+  return SourceLocation(p.source, p.line, p.column);
+}
+
 void
 ASTBacktrace::create()
 {