ci: try UCRT for windows ruby-head builds

[flavorjones]

What problem is this PR intended to solve?

The 3.1.0.dev windows ruby installer uses UCRT, see #2268 for context. This gives Nokogiri and @larskanis a feedback loop.

[flavorjones]

@larskanis This looks like it might be a genuine failure on UCRT?

https://github.com/sparklemotion/nokogiri/runs/2848463493?check_suite_focus=true#step:7:50

[larskanis]

The failure happens when calling the XLST function date:date(). So the issue resides in libxslt pretty sure. In contrast to MSVCRT, UCRT has non ANSI-C compatible time functions. This already needed a fix in ffi. I guess that libxslt simply disables date+time functions on UCRT. I'll try to fix that.

[flavorjones]

@larskanis That's interesting! Looking at libexslt/date.c it seems like WITH_TIME is a compile-time macro:

#if defined(HAVE_TIME_H)					\
    && (defined(HAVE_LOCALTIME) || defined(HAVE_LOCALTIME_R))	\
    && (defined(HAVE_GMTIME) || defined(HAVE_GMTIME_R))		\
    && defined(HAVE_TIME)
#define WITH_TIME
#endif

I'll also note that it's fine when Nokogiri compiles it (--disable-system-libraries), but not when we use the UCRT system libraries (--enable-system-libraries), which I don't fully understand.

Anything I can do to help?

[flavorjones]

Also: I'd be fine with not fixing this. For example, when using a version of libxml2 that does not have iconv support compiled in, we skip the tests and expose that configuration as part of VERSION_INFO.

[flavorjones]

WDYT of the following solution:

• during Nokogiri initialization, call exsltDateDate(NULL)
• if the return value is NULL, set a ruby constant like NOKOGIRI_LIBXSLT_TIME_SUPPORT to false
• else set it to true
• expose it in VERSION_INFO

Then we can either rewrite the failing test to not depend on date/time functionality, and/or conditionally run tests based on the value of the constant.

[larskanis]

I opened a PR on Mingw-packages addressing the date/time issue: msys2/MINGW-packages#8957

[flavorjones]

@larskanis In the meantime, I have a commit on this PR to detect whether libxslt is built with date-time functionality, and skip the assertion if not.

[larskanis]

The latest MSYS2 package mingw-w64-ucrt-x86_64-libxslt-1.1.34-4 is now in the official repository and it fixes the date/time issue on UCRT64.

[flavorjones]

@larskanis yup! looks good in this build: https://github.com/sparklemotion/nokogiri/runs/2873137424#step:7:35