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/development/libraries/gettext/gettext-setup-hook.sh

@@ -1,6 +1,8 @@
 gettextDataDirsHook() {
+    # See pkgs/build-support/setup-hooks/role.bash
+    getHostRoleEnvHook
     if [ -d "$1/share/gettext" ]; then
-        addToSearchPath GETTEXTDATADIRS "$1/share/gettext"
+        addToSearchPath "GETTEXTDATADIRS${role_post}" "$1/share/gettext"
     fi
 }
 
@@ -8,21 +10,8 @@ addEnvHooks "$hostOffset" gettextDataDirsHook
 
 # libintl must be listed in load flags on non-Glibc
 # it doesn't hurt to have it in Glibc either though
-gettextLdflags() {
-    # 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+=" -lintl"
-}
-
 if [ ! -z "@gettextNeedsLdflags@" ]; then
-    addEnvHooks "$hostOffset" gettextLdflags
+    # See pkgs/build-support/setup-hooks/role.bash
+    getHostRole
+    export NIX_${role_pre}LDFLAGS+=" -lintl"
 fi