gcr: Define _GNU_SOURCE

This ensures that definitions of functions e.g. getpass() are correctly
sourced from system headers, since it depends on feature test macros

(From OE-Core rev: 0d117e5d17c491e1d26aefb4b919410b07fd5347)

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-gnome/gcr/gcr_3.40.0.bb

@@ -13,6 +13,8 @@ DEPENDS = "p11-kit glib-2.0 libgcrypt gnupg-native \
 
 CACHED_CONFIGUREVARS += "ac_cv_path_GPG='gpg2'"
 
+CFLAGS += "-D_GNU_SOURCE"
+
 GNOMEBASEBUILDCLASS = "meson"
 GTKDOC_MESON_OPTION = "gtk_doc"
 inherit gnomebase gtk-icon-cache gtk-doc features_check upstream-version-is-even vala gobject-introspection gettext mime mime-xdg