[libcxx] Add test to check min/max requirement to regular expression

This commit adds tests that repeated characters in regular expressions
are within numeric limits, and that a <= b in a regex like `x{a,b}`.

Thanks to Andrey Maksimov for the patch.

Differential Revision: https://reviews.llvm.org/D62816

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@362525 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed