Merge #1901: add preFixupPhases to stdenv; for gsettings

Without this stdenv change it seems difficult to fix some glib's gsettings issues,
as the folders in question may (not) be created in installPhase.

pkgs/development/libraries/glib/setup-hook.sh

@@ -0,0 +1,17 @@
+# Install gschemas, if any, in a package-specific directory
+installFlagsArray+=("gsettingsschemadir=$out/gsettings-schemas/$name/glib-2.0/schemas/")
+
+make_glib_find_gsettings_schemas() {
+	# For packages that need gschemas of other packages (e.g. empathy)
+	if [ -d "$1/gsettings-schemas/*/glib-2.0/schemas" ]; then
+		addToSearchPath GSETTINGS_SCHEMAS_PATH "$1/gsettings-schemas/"*
+	fi
+}
+
+envHooks+=(make_glib_find_gsettings_schemas)
+
+glibPreFixupPhase() {
+	addToSearchPath GSETTINGS_SCHEMAS_PATH "$out/gsettings-schemas/$name"
+}
+
+preFixupPhases="$preFixupPhases glibPreFixupPhase"