wasm: support more vendor libraries

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

vendor/libc/libc.odin

@@ -0,0 +1,25 @@
+package odin_libc
+
+import "base:runtime"
+
+import "core:mem"
+
+@(private)
+g_ctx: runtime.Context
+@(private)
+g_allocator: mem.Compat_Allocator
+
+@(init)
+init_context :: proc() {
+	g_ctx = context
+
+	// Wrapping the allocator with the mem.Compat_Allocator so we can
+	// mimic the realloc semantics.
+	mem.compat_allocator_init(&g_allocator, g_ctx.allocator)
+	g_ctx.allocator = mem.compat_allocator(&g_allocator)
+}
+
+// NOTE: the allocator must respect an `old_size` of `-1` on resizes!
+set_context :: proc(ctx := context) {
+	g_ctx = ctx
+}