TryTableArgs only needs catches for try_table instructions. Reuse the
structured-instruction layout with catch storage in place of the else
target, and keep the catch elements in a FixedArray.
This avoids storing a full Vector inline in every Instruction variant
alternative and keeps the catch storage copyable for the variant.
Validation always fills structured instruction metadata before compiled
expressions are executed. Store the metadata directly instead of using
Optional, and update execution and printing paths accordingly.
Wasm opcodes only need one byte plus a 24-bit selector for
prefixed instructions. Store them in u32 instead of u64 and reject
selectors that would not fit. Update the Rust opcode generator to
accept the new integer suffixes used by Opcode.h.
On macOS, the cranelift JIT compilation step works by creating an
anonymous shared memory segment via shm_open() in the parent process
and passing the fd as an argument to the spawned cranelift-compiler
child. POSIX requires shm_open() to set FD_CLOEXEC on the returned
fd, which caused the child to immediately fail with EBADF when it
tried to read from the inherited fd number.
Clear FD_CLOEXEC after shm_open() so the fd actually survives the
spawn. The Linux memfd_create() path is unaffected since we call it
with flags=0 (no MFD_CLOEXEC), and Windows passes an inheritable
HANDLE instead of an fd.
