debian: Install lld on ARMv7

It turns out that lld is pretty much the only functional linker for ARMv7.

Facilitates fixing of ghc#21875 (closed).

images/debian.dhall

@@ -245,7 +245,7 @@ let debian10Images: List Image.Type =
     , bootstrapGhc = { version = "9.2.2", triple = "armv7-deb10-linux" }
     , llvm = Some (Llvm.Source.FromBindist { version = "11.0.1" , triple = "armv7a-linux-gnueabihf" })
     , cabalSource = (Cabal.Type.FromBindist "https://downloads.haskell.org/~ghcup/unofficial-bindists/cabal/3.6.2.0/cabal-install-3.6.2.0-armv7-linux-deb10.tar.xz")
-    , extraPackages = [ "libnuma-dev" ] # debianBuildDepends
+    , extraPackages = [ "libnuma-dev", "lld" ] # debianBuildDepends
     , withStack = False
     }
     -- N.B. Need GHC bindist for deb10 i386