treewide: Use pkgs/build-support/roles.bash to remove copy pasta

Also fix some setup hooks that unnecessarily used environment hooks,
which revolted in the same variable being modified too many times.

pkgs/os-specific/linux/musl/fts-setup-hook.sh

@@ -1,17 +1,4 @@
-ftsLdflags() {
-    # The `depHostOffset` describes how the host platform of the dependencies
-    # are slid relative to the depending package. It is brought into scope of
-    # the environment hook defined as the role of the dependency being applied.
-    case $depHostOffset in
-        -1) local role='BUILD_' ;;
-        0)  local role='' ;;
-        1)  local role='TARGET_' ;;
-        *)  echo "cc-wrapper: Error: Cannot be used with $depHostOffset-offset deps" >2;
-            return 1 ;;
-    esac
-
-    export NIX_${role}LDFLAGS+=" -lfts"
-}
-
-addEnvHooks "$hostOffset" ftsLdflags
+# See pkgs/build-support/setup-hooks/role.bash
+getHostRole
 
+export NIX_${role_pre}LDFLAGS+=" -lfts"

pkgs/os-specific/linux/musl/fts.nix

@@ -12,5 +12,8 @@ stdenv.mkDerivation rec {
 
   nativeBuildInputs = [ autoreconfHook pkgconfig ];
 
-  setupHook = ./fts-setup-hook.sh;
+  setupHooks = [
+    ../../../build-support/setup-hooks/role.bash
+    ./fts-setup-hook.sh
+  ];
 }