Cherry-pick: ICU-20309 "#if !UCONFIG_NO_CONVERSION" block should include the doxygen doc for uregex_openC

Pull request:
https://github.com/unicode-org/icu/pull/309

The pull request has been approved upstream.

Test: Treehugger
Change-Id: Ia7c3ee02e0be623aac5056b84b3649a3123b2061
1 file changed