gcc builds: reenable -Wstrict-overflow

[rlibby]

Summary

Relegate -Wno-error=strict-overflow to the zic makefile, as zic is the
only thing that needs it, and even zic appears now to be fixed upstream.

Test Plan

make buildworld buildkernel with amd64-gcc (gcc 6.3.0)
make tinderbox

[ngie]

When will zic(8) be fixed?

[rlibby]

In D12284#254856, @ngie wrote:

When will zic(8) be fixed?

It appears to have been in upstream: ftp://ftp.iana.org/tz/code/zic.c (see oadd).

As for when we might sync with upstream next, I have no idea. Last sync appears to have been in 2010.

[emaste]

In D12284#254878, @rlibby wrote:

It appears to have been in upstream: ftp://ftp.iana.org/tz/code/zic.c (see oadd).

As for when we might sync with upstream next, I have no idea. Last sync appears to have been in 2010.

We could also bring in that fix independently, in advance of a full update.

[rlibby]

In D12284#254932, @emaste wrote:

In D12284#254878, @rlibby wrote:

It appears to have been in upstream: ftp://ftp.iana.org/tz/code/zic.c (see oadd).

As for when we might sync with upstream next, I have no idea. Last sync appears to have been in 2010.

We could also bring in that fix independently, in advance of a full update.

We could, sort of. We could bring in the (now-out-of-date) fix from the 2012g version, before the signature of oadd changed. I don't think we can easily bring in the up-to-date code for just this.

I'm not sure it would be good to add to our (already significant) diff against the base. But here's what it would look like:

$ git diff
diff --git a/contrib/tzcode/zic/zic.c b/contrib/tzcode/zic/zic.c
index 00043b7940e7..39558b36a890 100644
--- a/contrib/tzcode/zic/zic.c
+++ b/contrib/tzcode/zic/zic.c
@@ -2484,37 +2484,27 @@ register char * cp;
 }
 
 static long
-oadd(t1, t2)
-const long     t1;
-const long     t2;
+oadd(const long t1, const long t2)
 {
-       register long   t;
-
-       t = t1 + t2;
-       if ((t2 > 0 && t <= t1) || (t2 < 0 && t >= t1)) {
+       if (t1 < 0 ? t2 < LONG_MIN - t1 : LONG_MAX - t1 < t2) {
                error(_("time overflow"));
                exit(EXIT_FAILURE);
        }
-       return t;
+       return t1 + t2;
 }
 
 static zic_t
-tadd(t1, t2)
-const zic_t    t1;
-const long     t2;
+tadd(const zic_t t1, const long t2)
 {
-       register zic_t  t;
-
        if (t1 == max_time && t2 > 0)
                return max_time;
        if (t1 == min_time && t2 < 0)
                return min_time;
-       t = t1 + t2;
-       if ((t2 > 0 && t <= t1) || (t2 < 0 && t >= t1)) {
+       if (t1 < 0 ? t2 < min_time - t1 : max_time - t1 < t2) {
                error(_("time overflow"));
                exit(EXIT_FAILURE);
        }
-       return t;
+       return t1 + t2;
 }
 
 /*

Personally I'd rather just move the warning suppression for now as it maintains the status quo and avoids making life harder for whoever eventually syncs this. Thoughts?

[rlibby]

@emaste suggested out of band to verify with a universe build. I did a make tinderbox and it succeeded.