fix(ghdl): put --std flag in front of all the others

This MR changes the order of the Flags passed to GHDL; spec for the language standards always comes first. The reason for that is that via ::fwfwk::tool::Flags (as well as the respective env var) the developer is able to change/define the flags to be used; however, there is a specific one (-frelaxed) which must come after --std to take effect (see https://ghdl.github.io/ghdl/using/InvokingGHDL.html#cmdoption-ghdl-frelaxed). Note that -frelaxed is required e. g. when Xilinx netlists are part of the simulation.