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ARROW-12094: [C++][R] Fix re2 building on clang/libc++

Also includes a followup to ARROW-11736 to add the utf8proc/re2 features to arrow_info() and use that in skip_if_not_available().

Closes #9811 from nealrichardson/re2-cran

Authored-by: Neal Richardson <neal.p.richardson@gmail.com>
Signed-off-by: Neal Richardson <neal.p.richardson@gmail.com>