Add spdlog (see #2210) (#2212)
Add spdlog (see #2210) (#2212)

* Add spdlog (see #2210), needs compiler-explorer/infra#403, and ideally a way of adding -DSPDLOG_COMPILED_LIB

* add spdlog compiler define

Co-authored-by: Patrick Quist <dda891045ad113066162ac923a134da212eb3ba7@gmail.com>
dkm/gcc-explorer,dkm/gcc-explorer,mattgodbolt/compiler-explorer,mattgodbolt/compiler-explorer,mattgodbolt/compiler-explorer,mattgodbolt/gcc-explorer,mattgodbolt/compiler-explorer,mattgodbolt/gcc-explorer,dkm/gcc-explorer,dkm/gcc-explorer,dkm/gcc-explorer,mattgodbolt/compiler-explorer,mattgodbolt/compiler-explorer,mattgodbolt/gcc-explorer,mattgodbolt/gcc-explorer,mattgodbolt/gcc-explorer,dkm/gcc-explorer,mattgodbolt/compiler-explorer,dkm/gcc-explorer,dkm/gcc-explorer,dkm/gcc-explorer,mattgodbolt/compiler-explorer