wasi: make the demo run on wasi and run it in CI

base/runtime/entry_wasm.odin

@@ -22,6 +22,11 @@ when !ODIN_TEST && !ODIN_NO_ENTRY_POINT {
 		@(link_name="_start", linkage="strong", require, export)
 		_start :: proc "c" () {
 			context = default_context()
+
+			when ODIN_OS == .WASI {
+				_wasi_setup_args()
+			}
+
 			#force_no_inline _startup_runtime()
 			intrinsics.__entry_point()
 		}

base/runtime/os_specific_wasi.odin

@@ -2,10 +2,54 @@
 //+private
 package runtime
 
-import "core:sys/wasm/wasi"
+foreign import wasi "wasi_snapshot_preview1"
+
+@(default_calling_convention="contextless")
+foreign wasi {
+	fd_write :: proc(
+		fd: i32,
+		iovs: [][]byte,
+		n: ^uint,
+	) -> u16 ---
+
+	@(private="file")
+	args_sizes_get :: proc(
+		num_of_args:  ^uint,
+		size_of_args: ^uint,
+	) -> u16 ---
+
+	@(private="file")
+	args_get :: proc(
+		argv:     [^]cstring,
+		argv_buf: [^]byte,
+	) -> u16 ---
+}
 
 _stderr_write :: proc "contextless" (data: []byte) -> (int, _OS_Errno) {
-	data_iovec := (wasi.ciovec_t)(data)
-	n, err := wasi.fd_write(1, {data_iovec})
+	n: uint
+	err := fd_write(1, {data}, &n)
 	return int(n), _OS_Errno(err)
 }
+
+_wasi_setup_args :: proc() {
+	num_of_args, size_of_args: uint
+	if errno := args_sizes_get(&num_of_args, &size_of_args); errno != 0 {
+		return
+	}
+
+	err: Allocator_Error
+	if args__, err = make([]cstring, num_of_args); err != nil {
+		return
+	}
+
+	args_buf: []byte
+	if args_buf, err = make([]byte, size_of_args); err != nil {
+		delete(args__)
+		return
+	}
+
+	if errno := args_get(raw_data(args__), raw_data(args_buf)); errno != 0 {
+		delete(args__)
+		delete(args_buf)
+	}
+}

base/runtime/wasm_allocator.odin

@@ -760,7 +760,7 @@ free :: proc(a: ^WASM_Allocator, ptr: rawptr, loc := #caller_location) {
 	defer unlock(a)
 
 	size := region.size
-	assert(region_is_in_use(region), "double free", loc=loc)
+	assert(region_is_in_use(region), "double free or corrupt region", loc=loc)
 
 	prev_region_size_field := ([^]uint)(region)[-1]
 	prev_region_size := prev_region_size_field & ~uint(FREE_REGION_FLAG)