fix_run: symbol census on the gated, kernel-style-compiled object
(recorded by build.sh '== fix validation' on the guest; see build.log / fix_build.log)

-- baseline: ungated verbatim body, out-of-line object defines the symbol:
0000000000000000 T k_ffsl

-- patched: f_ffsl_gated.c compiled kernel-style (-D_KERNEL, cpufunc.h in effect):
FIXCOMPILE-OK: gated ffsl.c compiles kernel-style; global ffsl symbols in object: 0 (body compiles away on x86_64)