Fix links for now.

Author: mark-i-m

src/appendix/background.md

@@ -286,7 +286,7 @@ does not.
 - [Practical Foundations for Programming Languages](https://www.cs.cmu.edu/~rwh/pfpl/2nded.pdf)
 - [Compilers: Principles, Techniques, and Tools, 2nd Edition](https://www.pearson.com/us/higher-education/program/Aho-Compilers-Principles-Techniques-and-Tools-2nd-Edition/PGM167067.html)
 - [Garbage Collection: Algorithms for Automatic Dynamic Memory Management](https://www.cs.kent.ac.uk/people/staff/rej/gcbook/)
-- [Linkers and Loaders](https://linker.iecc.com/)
+- [Linkers and Loaders](https://www.amazon.com/Linkers-Kaufmann-Software-Engineering-Programming/dp/1558604960) (There are also free versions of this, but the version we had linked seems to be offline at the moment.)
 - [Advanced Compiler Design and Implementation](https://www.goodreads.com/book/show/887908.Advanced_Compiler_Design_and_Implementation)
 - [Building an Optimizing Compiler](https://www.goodreads.com/book/show/2063103.Building_an_Optimizing_Compiler)
 - [Crafting Interpreters](http://www.craftinginterpreters.com/)