[PATCH 1/2] Merge mktime, timegm from upstream Gnulib

[Paul Eggert]

Florian Weimer wrote:
> It happens for the /usr/share/zoneinfo/America/Sao_Paulo file from
> tzdata-2018e-1.fc27.  So the test case is not properly isolated, either.

The test case should work regardless of what's in that file, and should work 
even if that file does not exist or if there's an I/O error reading it. As I 
vaguely recall, the original bug report was against TZ=America/Sao_Paulo and 
that's why the test case uses that particular setting.

It'd probably be good to add "<-03>3<-02>,M11.1.0/0,M2.3.0/0" to the tz_strings 
array in that test case, to do a southern-hemisphere-style test even if the 
Sao_Paulo file contains garbage or does not exist. I don't recall the original 
problem well enough to know whether such an addition to tz_strings would suss 
out the Sao_Paulo bug.