[OPENMP]Fix PR46170: partial mapping for array sections of data members.

Summary:
If the data member is mapped as an array section, need to emit the
pointer to the last element of this array section and use this pointer
as the highest element in partial struct data.

Reviewers: jdoerfert

Subscribers: yaxunl, guansong, sstefan1, cfe-commits, caomhin

Tags: #clang

Differential Revision: https://reviews.llvm.org/D81037