[OpenMP] Fix GCC build issues and restore "Additional APIs used by the MSVC...

[OpenMP] Fix GCC build issues and restore "Additional APIs used by the MSVC compiler for loop collapse (rectangular and non-rectangular loops)"

Fixes a GCC build issue (an instance of unallowed typename keyword) and reworks memory allocation
to avoid the use of C++ library based primitives ) in and restores the earlier commit https://reviews.llvm.org/D148393

Differential Revision: https://reviews.llvm.org/D149010