Fix "ghdl.flags" error in documentation

[LukasVik]

I believe this must be a copy-paste error. "ghdl.flags" is for compilation options, and is documented as such further up in the file. "ghdl.elab_flags" and "ghdl.sim_flags", which are for simulation options are documented below.

[eine]

Hi @LukasVik! I agree with fixing the location of that flag, however, I think that your interpretation might not be correct. I'd say that ghdl.flags is used both for compilation and simulation. Then, you can have extra elab flags and extra run flags. Hence, I think that the flag in section "Simulation options" should be moved down, together with other ghdl.* flags in the same section. But it should not be removed. Furthermore, it might be desirable to change the description so that "..passed to ghdl -a and ghdl --elab-run commands..." is said.

[eine]

Upon inspection of the sources (https://github.com/VUnit/vunit/blob/master/vunit/sim_if/ghdl.py) I was wrong and your interpretation is correct. I must have been mislead by some wip I have somewhere... So, I'm ok with with this PR.

@LarsAsplund, @kraigher, should we consider to rename ghdl.flags to, say, ghdl.analysis_flags in order to avoid this ambiguity. This would be breaking a change, so we might keep ghdl.flags as an alias.

[LukasVik]

Upon inspection of the sources (https://github.com/VUnit/vunit/blob/master/vunit/sim_if/ghdl.py) I was wrong and your interpretation is correct. I must have been mislead by some wip I have somewhere... So, I'm ok with with this PR.

Yeah it threw me for a loop as well. Had to inspect the code to find what was what.

should we consider to rename ghdl.flags to, say, ghdl.analysis_flags in order to avoid this ambiguity. This would be breaking a change, so we might keep ghdl.flags as an alias.

Makes sense. The current naming is confusing, as proven by this conversation.

[kraigher]

If we change the name the old name must still work but have a deprecation message for many releases before we remove it.