ticket:10274: Add compound duration formatting for C++

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk@33986 251d0590-4201-4cf1-90de-194747b24ca1
ticket:10258: Parse different variations of '+' and '-' when isLenient is set in C++.

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk@33989 251d0590-4201-4cf1-90de-194747b24ca1
ticket:10271 tweak to configure test for C++11 #include <atomic>.

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk@33992 251d0590-4201-4cf1-90de-194747b24ca1