Fix memory leaks in WASI setjmp handler

[white-axe]

This pull request fixes two memory leaks in the implementation of setjmp in WASI (WebAssembly) builds of Ruby:

• The first commit fixes a problem where the stack pointer is not reset after a longjmp, leading to leaking of parts of the stack. This also causes leaking of Ruby objects since the garbage collector looks for GC roots on the stack.
• The second commit fixes a problem where the VM jump buffers are not freed after a longjmp. In WASI builds of Ruby, jump buffers are allocated on the heap instead of on the stack, so they need to be manually deallocated. I changed the implementations of rb_vm_tag_jmpbuf_init() and rb_vm_tag_jmpbuf_deinit() to clean up leaked jump buffers before initializing/deinitializing jump buffers.

[white-axe]

@kateinoigakukun, since you maintain the WASI builds of Ruby, can you take a look at this?

[kateinoigakukun]

Let me execute ruby.wasm test suite with this change: ruby/ruby.wasm#586

[white-axe]

Here's a test to see if a WASI build is affected by these two memory leaks. This script causes all of the current WASI builds from https://github.com/ruby/ruby.wasm to rapidly consume around 800 mebibytes of memory due to the jump buffer leak and then crash from what I believe is stack buffer overflow caused by the stack pointer leak:

loop do
  array = [0]
  for item in array
    break
  end
end

To test it out, save it as test.rb in the current working directory, and then:

curl -Lo ruby.tar.gz https://github.com/ruby/ruby.wasm/releases/download/2.7.1/ruby-3.4-wasm32-unknown-wasip1-full.tar.gz
tar xzf ruby.tar.gz --strip-components=1
wasmtime --dir .::/ usr/local/bin/ruby test.rb

[kateinoigakukun]

Really good catch, the patch looks good to me.

[kateinoigakukun]

Hi @white-axe, the change seems causing OOM on ruby.wasm test suite, so I'm reverting this for now #13026

[white-axe]

I'll find some other way to fix the second memory leak then