[libcxx] Recover no-exceptions XFAILs - I

First batch of changes to get some of these XFAILs working in the
no-exceptions libc++ variant.

Changed some XFAILs to UNSUPPORTED where the test is all about exception
handling. In other cases, used the test macros TEST_THROW and
TEST_HAS_NO_EXCEPTIONS to conditionally exclude those parts of the test
that concerns exception handling behaviour.

Reviewers: EricWF, mclow.lists

Differential revision: https://reviews.llvm.org/D24562

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@283441 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/re/re.regex/re.regex.construct/bad_repeat.pass.cpp

@@ -7,7 +7,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// XFAIL: libcpp-no-exceptions
+// UNSUPPORTED: libcpp-no-exceptions
 // <regex>
 
 // template <class charT, class traits = regex_traits<charT>> class basic_regex;