fix validation (kernel-style compile of gated variants + symbol census)
In file included from /usr/src/sys/sys/libkern.h:51,
                 from f_ffsl_gated.c:32:
/usr/src/sys/sys/systm.h:216:5: warning: conflicting types for built-in function 'log' [-Wbuiltin-declaration-mismatch]
 int log (int, const char *, ...) __printflike(2, 3);
     ^~~
In file included from /usr/src/sys/sys/libkern.h:51,
                 from f_flsl_gated.c:32:
/usr/src/sys/sys/systm.h:216:5: warning: conflicting types for built-in function 'log' [-Wbuiltin-declaration-mismatch]
 int log (int, const char *, ...) __printflike(2, 3);
     ^~~
In file included from /usr/src/sys/sys/libkern.h:51,
                 from f_flsll_gated.c:32:
/usr/src/sys/sys/systm.h:216:5: warning: conflicting types for built-in function 'log' [-Wbuiltin-declaration-mismatch]
 int log (int, const char *, ...) __printflike(2, 3);
     ^~~