[Patch] Fortran/OpenMP: Add parsing support for allocators/allocate directive (was: [Patch] Fortran/OpenMP: Add parsing support for allocators directive)

Related pending (simple) patches - aka *Patch Ping*: * [Patch] Fortran: Extend align-clause checks of OpenMP's allocate clause https://gcc.gnu.org/pipermail/gcc-patches/2022-December/608401.html * [Patch] OpenMP: Parse align clause in allocate directive in C/C++ https://gcc.gnu.org/pipermail

[Patch] Fortran/OpenMP: Add parsing support for allocators directive

This patch adds parsing/argument-checking support for '!$omp allocators allocate([align(int),allocator(a) :] list)' This is kind of logical follow-up and prep patch for the '!$omp allocate(list) [align(v) allocator(a)]' support that was submitted as part of a larger patchset by Abid; cf. revi