[OG12][committed] openmp: Add support for the 'present' modifier

[Kwok Cheung Yeung]

Hello

I've ported my patch for supporting the OpenMP 5.1 'present' modifier 
and committed it to the devel/omp/gcc-12 development branch:

229b705862c openmp: Add support for the 'present' modifier

Tested with offloading on amdgcn and nvptx.

Kwok