Cherry-pick ICU-20975 BRS66rc Fix warnings found when building ICU4C samples.

Cherry-pick upstream commit
https://github.com/unicode-org/icu/commit/e1aa9119ad37ff1ea727ee42afb13c64d7f14170

Test: n/a
Change-Id: I0d05749af559da6cb7c4e7877fcfcb2006fbc4f2
2 files changed