databases/postgresql16-client does not build

[Marc Baudoin <babafou%babafou.eu.org@localhost>]

Hi,

While trying to compile databases/postgresql16-client:

[...]
checking whether to build with ICU support... yes
checking for icu-uc icu-i18n... no
configure: error: ICU library not found
If you have ICU already installed, see config.log for details on the
failure.  It is possible the compiler isn't looking in the proper directory.
Use --without-icu to disable ICU support.
*** Error code 1

Stop.
make[1]: stopped in /usr/pkgsrc/databases/postgresql16-client

ICU doesn't seem to be listed as a dependency of this package.