FR: add a system allowing to define the linker to invoke
Because of #31066 if the system is configured to use ld.gold as linker, FPC fails to link programs. For example here, on Fedora linux, I have to use `alternatives --config ld` each time I start Lazarus. There should be a way to configure the particular linker that FPC invokes, either (sorted by descending personnal preference) - an entry in the configuration file - using the `LD` env variable - a compiler flag, e.g `fpc <usual args...> --linker=ld.bfd`
issue