0.9.1 --- the second register comes back from every call

[Sunrisepeak]

Every program built with --release over openkal-macos faulted before main.

Found through lsp-mcpp: the release server, and a minimal import std; std::println program over openkal-llvm-runtime 0.9.4, both stop in the C library's initializer on macos-14:

* thread #1, stop reason = EXC_BAD_ACCESS (code=1, address=0x0)
  * frame #0: kal_fs_preopen + 288        ldrb w11, [x10], #0x1    ; x10 = 0
    frame #1: okm_table_init + 608
    frame #2: __okm_libc_init + 400
    frame #3: dyld ... findAndRunAllInitializers

This kernel returns a second value in x1 from every system call (rdx on x86_64) and writes it whether or not the call has one; duplicate() and pipe_pair() already read it. The generic sys() declared x1 an input only, so an optimizing compiler assumed it survived the call. The release table(), disassembled:

adrp  x1, "/"@PAGE ; add x1, x1, "/"@PAGEOFF    ; path argument of openat
svc   #0x80                                     ; the kernel clears x1
...
stp   x1, x9, [x8]                              ; t[1] = { x1, 1 }  -> name == NULL

kal_fs_preopen(1) then copied the name from address zero. The dev profile keeps nothing in a register across a call, which is why it never showed.

• src/sys.h: x1 is an output of sys() as well as an input on arm64, and rdx on x86_64. Compiled with -O2, table() now keeps "/" in a callee-saved register across the call.
• -fno-builtin beside -fno-exceptions -fno-rtti -fno-stack-protector: the same release build turned okm::length into a call to strlen, a C library symbol this package does not reference by design (openkal-windows 0.7.1 made the same change for the same reason).
• CI: this package's own tests and the "objects reference nothing of a C library" check run in the dev and release profiles; conformance_process_task enumerates every preopen and is what would have failed.
• 0.9.1.

Every source compiles with -O2 for arm64 and x86_64 macOS, and the arm64 object has no undefined strlen. The release rows of this CI are the measurement on the machine itself.