backport ICU-20575 to fix err/crasher in ICU 64.x

[srl295]

• Subsystem: deps

Tracking: unicode-org/icu#634
Now that #27361 (ICU 64.2) landed, it would be good to pull this in.

This probably exacerbated #27379 on some platforms.

[srl295]

fyi @targos @refack

[srl295]

Test case:

env LANG=fr@EURO ./out/Debug/node -p 'new Intl.NumberFormat().resolvedOptions().locale

Crashes with:

Fatal error in ../../deps/v8/src/objects/intl-objects.cc, line 417

Locale::forLocaleTag("fr-x-lvariant-euro-euro") returns U_ILLEGAL_ARGUMENT_ERROR (why? Perhaps an illegal doubled tag.)

After the fix the printout is fr-x-lvariant-euro

(for unknown reasons, v8 patched around some of the other behaviors, so the output will look different than the upstream issue.)

[targos]

Fixed in #27435