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: Ida28f7c955959565a2133242b826bb5038758407
Reviewed-on: https://gerrit.libreoffice.org/2576Reviewed-by: Fridrich Strba <fridrich@documentfoundation.org>
Tested-by: Fridrich Strba <fridrich@documentfoundation.org>