wasm: support more vendor libraries

Adds support for:
- box2d
- cgltf
- stb image
- stb rect pack

vendor/libc/README.md

@@ -0,0 +1,12 @@
+# vendor:libc
+
+A (very small) subset of a libc implementation over Odin libraries.
+This is mainly intended for use in Odin WASM builds to allow using libraries like box2d, cgltf etc. without emscripten hacks.
+
+You can use this with clang by doing `clang -c --target=wasm32 --sysroot=$(odin root)/vendor/libc` (+ all other flags and inputs).
+This will (if all the libc usage of the library is implemented) spit out a `.o` file you can use with the foreign import system.
+If you then also make sure this package is included in the Odin side of the project (`@(require) import "vendor:libc"`) you will be able
+compile to WASM like Odin expects.
+
+This is currently used by `vendor:box2d`, `vendor:stb/image`, `vendor:stb/truetype`, `vendor:stb/rect_pack`, and `vendor:cgltf`.
+You can see how building works by looking at those.