[OpenMP][NFC] Move debug declares into CMAKE out of "private.h" (#73732)

Everywhere else we define this in the CMakeLists.txt and "private.h"
needs to go. Rename "Libomptarget" into "omptarget", no benefit from
"lib".

GitOrigin-RevId: 5d57041d39461d0262fcef71bd9cfa0ee20c6576
24 files changed