CI: Replace old GDC script with matrix job

[Geod24]

Since COVERAGE is always false, this never ran. With an up-to-date GDC now available, we can re-enable it.

[Geod24]

Needs https://github.com/dlang-community/setup-dlang/pull/57 merged & released

[Geod24]

So OpenSSL doesn't support gdc. This can be worked around with something like:

+// Used by the CI
+configuration "library-nonet-gdc" {
+       dependency "vibe-d:http" version=">=0.9.0 <0.10.0"
+    dependency "openssl" version="~>3.0"
+    subConfiguration "openssl" "library-manual-version"
+       targetType "library"
+       excludedSourceFiles "source/app.d"
+}

but then, I found out that -Werror turns on -Werror=deprecated, so essentially -de, which makes GDC a bit unusable (!). CC @ibuclaw . Will see what we can do on dub side when I get a bit of free time.

[ibuclaw]

but then, I found out that -Werror turns on -Werror=deprecated, so essentially -de, which makes GDC a bit unusable (!). CC @ibuclaw . Will see what we can do on dub side when I get a bit of free time.

DMD is the weird one for having a split brain between warnings and deprecations. It's all warnings as far as gcc diagnostics are concerned.

[WebFreak001]

issue is here: https://github.com/dlang/dub/runs/7418736496?check_suite_focus=true#step:8:76

it tries to run gdc -run which doesn't exist, probably need to adjust a test here.