Missing OpenMP support for P3M macOS binaries (affects data.table, fixest, and likely others)

Background Since R 4.3.0, CRAN has shipped an OpenMP runtime with its macOS distribution of R. This means that packages can support multithreading out of the box on Mac without users needing to configure ~/.R/Makevars and/or install from source (see OpenMP on macOS with Xcode tools). Several packages have already taken advantage of this by shipping configure scripts that detect the OpenMP runtime at build time and enable the appropriate compiler/linker flags. For example: data.table (PR #603...