Cannot make LDC use LTO when called via DUB

[Nordlöw]

On Saturday, 23 September 2017 at 15:19:09 UTC, Nordlöw wrote:
> I've added
>
> buildType "release" {
>          buildOptions "releaseMode" "optimize" "inline"
>          dflags-posix-ldc "-flto=thin" "-Xcc=-fuse-ld=gold"
> }
>
> to my dub.sdl and built (on Linux) as
>
>     /usr/bin/dub -v run --compiler=ldc2 --build=release
>
> but neither the flag "-flto=thin" nor "-Xcc=-fuse-ld=gold" is 
> propagated to the ldc2 call (at least no printed on stdout).
>
> What's missing?

Neither

dflags-dmd "-xxx"
dflags-posix-dmd "-xxx"
dflags-linux-dmd "-xxx"

has any effect on my build (in dub.sdl).