#include <machine/cpufunc.h>, which may define inline versions of some

of the functions in libkern.  Without this, parts of the kernel would
reference a non-existent (undeclared and undefined) ffs() function; the
only reason this didn't break the kernel build is that gcc happens to
have a built-in ffs() and incorrectly fails to warn about the lack of
prototypes for built-in functions.

sys/sys/libkern.h

@@ -43,6 +43,8 @@
 #include <sys/systm.h>
 #endif
 
+#include <machine/cpufunc.h>
+
 /* BCD conversions. */
 extern u_char const	bcd2bin_data[];
 extern u_char const	bin2bcd_data[];