[OPENMP]Fix PR46688: cast the type of the allocated variable to the initial one.

Summary:
If the original variable is marked for allocation in the different
address space using #pragma omp allocate, need to cast the allocated
variable to its original type with the original address space.
Otherwise, the compiler may crash trying to bitcast the type of the new
allocated variable to the original type in some cases, like passing this
variable as an argument in function calls.

Reviewers: jdoerfert

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

Tags: #clang

Differential Revision: https://reviews.llvm.org/D83696