MFC r274847:

Fix the following -Werror warnings from clang 3.5.0, while building
usr.bin/locate:

usr.bin/locate/locate/util.c:249:29: error: taking the absolute value of unsigned type 'unsigned int' has no effect [-Werror,-Wabsolute-value]
                            MAXPATHLEN, abs(i) < abs(htonl(i)) ? i : htonl(i));
                                                 ^
usr.bin/locate/locate/util.c:249:29: note: remove the call to 'abs' since unsigned values cannot be negative
                            MAXPATHLEN, abs(i) < abs(htonl(i)) ? i : htonl(i));
                                                 ^~~
usr.bin/locate/locate/util.c:274:32: error: taking the absolute value of unsigned type 'unsigned int' has no effect [-Werror,-Wabsolute-value]
                            MAXPATHLEN, abs(word) < abs(htonl(word)) ? word :
                                                    ^
usr.bin/locate/locate/util.c:274:32: note: remove the call to 'abs' since unsigned values cannot be negative
                            MAXPATHLEN, abs(word) < abs(htonl(word)) ? word :
                                                    ^~~

The problem is that ntohl() always returns an unsigned quantity.  In
this case, it's expected to be cast back to a signed integer, but to
stop complaints about abs() we just store it into an integer, and don't
call ntohl() again.

Reviewed by:	ngie
Differential Revision: https://reviews.freebsd.org/D1196
MFC r274898:

Fix the following -Werror warnings from clang 3.5.0, while building
usr.sbin/rtadvd:

usr.sbin/rtadvd/rtadvd.c:1291:7: error: taking the absolute value of unsigned type 'unsigned int' has no effect [-Werror,-Wabsolute-value]
                    abs(preferred_time - pfx->pfx_pltimeexpire) > rai->rai_clockskew) {
                    ^
usr.sbin/rtadvd/rtadvd.c:1291:7: note: remove the call to 'abs' since unsigned values cannot be negative
                    abs(preferred_time - pfx->pfx_pltimeexpire) > rai->rai_clockskew) {
                    ^~~
usr.sbin/rtadvd/rtadvd.c:1324:7: error: taking the absolute value of unsigned type 'unsigned int' has no effect [-Werror,-Wabsolute-value]
                    abs(valid_time - pfx->pfx_vltimeexpire) > rai->rai_clockskew) {
                    ^
usr.sbin/rtadvd/rtadvd.c:1324:7: note: remove the call to 'abs' since unsigned values cannot be negative
                    abs(valid_time - pfx->pfx_vltimeexpire) > rai->rai_clockskew) {
                    ^~~
2 errors generated.

These warnings occur because both preferred_time and pfx_pltimeexpire
are uint32_t's, so the subtraction expression is also unsigned, and
calling abs() is a no-op.

However, the intention was to look at the absolute difference between
the two unsigned quantities.  Introduce a small static function to
clarify what we're doing, and call that instead.

Reviewed by:	hrs
Differential Revision: https://reviews.freebsd.org/D1197
MFC r274900:

Fix the following -Werror warnings from clang 3.5.0, while building
bsnmpd's snmp_hostres module:

usr.sbin/bsnmpd/modules/snmp_hostres/hostres_snmp.c:204:20: error: absolute value function 'abs' given an argument of type 'const long' but has parameter of type 'int' which may cause truncation of value [-Werror,-Wabsolute-value]
        str[9] = (u_char)(abs(tm->tm_gmtoff) / 3600);
                          ^
usr.sbin/bsnmpd/modules/snmp_hostres/hostres_snmp.c:204:20: note: use function 'labs' instead
        str[9] = (u_char)(abs(tm->tm_gmtoff) / 3600);
                          ^~~
                          labs
usr.sbin/bsnmpd/modules/snmp_hostres/hostres_snmp.c:205:22: error: absolute value function 'abs' given an argument of type 'const long' but has parameter of type 'int' which may cause truncation of value [-Werror,-Wabsolute-value]
        str[10] = (u_char)((abs(tm->tm_gmtoff) % 3600) / 60);
                            ^
usr.sbin/bsnmpd/modules/snmp_hostres/hostres_snmp.c:205:22: note: use function 'labs' instead
        str[10] = (u_char)((abs(tm->tm_gmtoff) % 3600) / 60);
                            ^~~
                            labs

Since tm::tm_gmtoff is a long, use labs(3) instead.
MFC r274724:
cxgbe(4): figure out the max payload size and save it for later.