Upstream changes
https://ssl.icu-project.org/trac/changeset/32865
https://ssl.icu-project.org/trac/changeset/32908

See also
https://bugzilla.redhat.com/show_bug.cgi?id=918167

Plus changed UMutex to UMTX to make these compile in icu49.

Change-Id: Ib5dba7085e6b2dd3925c0c220b5d264e4c7bb4c8