sysutils/gdisk: Unbreak UTF16 option

/usr/bin/ld: undefined reference to symbol `_ZN3icu13UnicodeStringC1EPKc' (try adding -licuuc)
//usr/local/lib/libicuuc.so.60: could not read symbols: Bad value

PR: 198518
Submitted by: Ting-Wei Lan <lantw44@gmail.com>
Approved by: wg (maintainer timeout, ~3 years)