Mention an alternative approach for toolchains

cf. WebAssembly#21

proposals/custom-page-sizes/Overview.md

@@ -358,6 +358,30 @@ This approach has the following benefits:
 
 [imagine]: https://github.com/WebAssembly/custom-page-sizes/issues/3
 
+#### Alternative: use an immutable global instead of the relocations
+
+Alternativey, we can probably use an immutable global instead of
+the relocations.
+
+Pros over relocations:
+
+- The toolchain implementations might be more straightforward that way.
+- A global can be exported/imported. It might be simpler for things like
+  [dynamic-linking].
+- The resulted binary might be more friendly to binary-rewriters like
+  wasm-opt.
+
+A possible downside is that you can't have the page size in data sections.
+Eg. consider a C global variable like the following.
+It shouldn't be a big problem these days as modern applications do not
+assume that the page size is a build-time constant anyway though.
+
+```c
+static int global_var = PAGE_SIZE;
+```
+
+[dynamic-linking]: https://github.com/WebAssembly/tool-conventions/blob/main/DynamicLinking.md
+
 ### How This Proposal Satisfies the Motivating Use Cases
 
 1. Does this proposal help Wasm better target resource-constrained environments,