mu-perf-benchmarks fib: movq $-2,%ECX

When trying to run my mu_fib_fast benchmark (python3 -m mubench local ./example/test_mu_fib.yml, in the latest version of mu-perf-benchmarks) on x86-64 I get the following errror:

INFO - executing: "clang" "example/fib_mu_fast-emit/mubench$cb_init.s" "example/fib_mu_fast-emit/mubench$cb_begin.s" "example/fib_mu_fast-emit/mubench$cb_end.s" "example/fib_mu_fast-emit/mubench$cb_report.s" "example/fib_mu_fast-emit/clockcb$tspec2dbl.s" "example/fib_mu_fast-emit/fib.s" "example/fib_mu_fast-emit/entry.s" "example/fib_mu_fast-emit/context.s" "example/fib_mu_fast-emit/main.c" "/home/isaacg/mu-impl-fast/target/release/libmu.a" "-ldl" "-lrt" "-lm" "-lpthread" "-rdynamic" "-o" "/root/mu-perf-benchmarks/example/fib-mu_fast"
INFO - ---out---
INFO -
INFO - ---err---
INFO - example/fib_mu_fast-emit/fib.s:44:11: error: invalid operand for instruction
        movq $-1,%ECX
                 ^~~~
example/fib_mu_fast-emit/fib.s:52:11: error: invalid operand for instruction
        movq $-2,%ECX
                 ^~~~

thread '<unnamed>' panicked at 'assertion failed: output.status.success()', src/testutil/mod.rs:41
stack backtrace:
   0: std::sys::imp::backtrace::tracing::imp::unwind_backtrace
             at /checkout/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::_print
             at /checkout/src/libstd/sys_common/backtrace.rs:71
   2: std::panicking::default_hook::{{closure}}
             at /checkout/src/libstd/sys_common/backtrace.rs:60
             at /checkout/src/libstd/panicking.rs:355
   3: std::panicking::default_hook
             at /checkout/src/libstd/panicking.rs:371
   4: std::panicking::rust_panic_with_hook
             at /checkout/src/libstd/panicking.rs:549
   5: std::panicking::begin_panic
   6: mu::testutil::exec
   7: mu::testutil::aot::link_primordial
   8: mu::vm::vm::VM::make_boot_image_internal
   9: mu::vm::api::api_bridge::_forwarder__MuCtx__make_boot_image
  10: main
  11: __libc_start_main
  12: _start
fatal runtime error: failed to initiate panic, error 5

It ran without error on aarch64 (assuming johns code actually checks that fib produces the right result)