[OpenMP][OMPT] Fix reported target pointer for data alloc callback

This patch fixes: https://github.com/llvm/llvm-project/issues/64671
DataOp EMI callbacks would not report the correct target pointer.
This is now alleviated by passing a `void**` into the function which
emits the actual callback, then evaluating that pointer.

Note: Since this is only done after the pointer has been properly
updated, only `endpoint=2` callbacks will show a non-null value.

Reviewed By: dhruvachak, jdoerfert

Differential Revision: https://reviews.llvm.org/D157996

(cherry picked from commit 41f3626f)