common: some FreeBSD headers are incomplete to avoid namespace pollution

In file included from src/common/x64/cpu_detect.cpp:16:
/usr/include/machine/cpufunc.h:66:17: error: unknown type name 'u_int'
static __inline u_int
                ^
/usr/include/machine/cpufunc.h:67:6: error: unknown type name 'u_int'
bsfl(u_int mask)
     ^
/usr/include/machine/cpufunc.h:69:2: error: unknown type name 'u_int'
        u_int   result;
        ^
/usr/include/machine/cpufunc.h:75:17: error: unknown type name 'u_long'; did you mean 'long'?
static __inline u_long
                ^
/usr/include/machine/cpufunc.h:76:6: error: unknown type name 'u_long'; did you mean 'long'?
bsfq(u_long mask)
     ^
/usr/include/machine/cpufunc.h:78:2: error: use of undeclared identifier 'u_long'; did you mean
      'long'?
        u_long  result;
        ^
[...]