In 2682e5f5, several instances of AC_HEADER_TIME were removed since
it is a deprecated autoconf macro. However, this was the macro that
defined TIME_WITH_SYS_TIME, which was used to indicate that <time.h>
can be included alongside <sys/time.h>. TIME_WITH_SYS_TIME is still
used in the configure test body and since it is no longer defined,
<time.h> is *not* included on systems that have <sys/time.h>.
In particular, at least on musl libc and glibc, <sys/time.h> does
not implicitly include <time.h> and does not declare clock_gettime,
gmtime_r, or localtime_r. This causes configure to fail to detect
those functions.
The AC_HEADER_TIME macro deprecation text says
> All current systems provide time.h; it need not be checked for.
> Not all systems provide sys/time.h, but those that do, all allow
> you to include it and time.h simultaneously.
So, to fix this issue, simply include <time.h> unconditionally when
testing for time-related functions and in libcurl, and don't bother
checking for it.
Closes#6859
eaa1d73229