vala: Fix global arguments for valac

[arteymix]

There's two things I would like to address here:

• add VALAFLAGS environment variable support
• fix global arguments provided by -Dvala_args which are not considered at this point

For VALAFLAGS, it is already supported by autotools and waf, so there's not excuse not to have it as well.

I tried to dig a bit into the code to see why the arguments weren't set, but couldn't find anything so far.

[jpakkane]

⚔ conflicts.

[arteymix]

@jpakkane It's not meant to be merged now, I still not have figured how to fix -Dvala_args.

[arteymix]

The only thing that is missing is passing -Dvala_args during the initial configure step with meson.py. Adding the flag after with mesonconf.py works as expected and the build considers VALAFLAGS as well.

[arteymix]

I fixed the precedence of arguments to follow what generate_basic_compiler_args does.

I still can't figure why arguments are not passed on the initial meson.py call.

[nirbheek]

What's the status of this now?

[arteymix]

@nirbheek I need to rebase the work and see if -Dvala_args have already been addressed elsewhere

[arteymix]

@nirbheek Everything is working! :)

I can't even get meson -Dc_args=-g to work. Is there any reason?

[nirbheek]

I didn't even know that was a thing, @jpakkane?

[arteymix]

@jpakkane Is it possible to schedule this PR for 0.40?

[jpakkane]

Please rebase so the tests are rerun. If they pass then we'll merge this.

[nirbheek]

@arteymix could you look at #1645 next? Allowing VALAC to set the vala compiler.