DMD release compiler flags when building with LDC

[Daniel Kozak]

On Wed, Oct 23, 2019 at 1:25 PM kinke via Digitalmars-d
<digitalmars-d at puremagic.com> wrote:
>
>...
> My bad, I thought build.d was a replacement for the Makefile,
> instead the Makefile is based on it, so this should kick in:
> https://github.com/dlang/dmd/blob/ce7576f256d4efaff843f5e7d6ed39e8d7f32a4e/src/build.d#L781-L784
>
> druntime is linked as machine code though, so an additional
> `-defaultlib=druntime-ldc-lto` (if available in the used LDC
> package, true for almost all official packages) would
> additionally enable LTO across DMD and druntime.

Not exactly, build.d has been use only for some part of dmd, so this
is reason why I have opened https://bugs.archlinux.org/task/63569.
There has been mismatch (some code has been compiled witl LTO and some
was not ). It is possible right now build.d is used for everything so
it could work.