cmake - silence cmake warning

DEPENDS is not accepted for TARGET in add_custom_command (CMP0175)

Behavior in old cmake: just ignore DEPENDS
Behavior starting from cmake 3.30: warn
The fix: remove DEPENDS

TARGET form requires exactly one of PRE_BUILD, PRE_LINK or POST_BUILD to be given (CMP0175)

Behavior in old CMAKE: assume POST_BUILD
Behavior starting from cmake 3.30: assume POST_BUILD but warn
The fix: explicitely set POST_BUILD