metacity: allow for warnings during compilation

Add a PACKAGECONFIG option which lets us permit warnings during
compilation until warnings from new compiler versions are
dealt with.

enable the packageconfig by default since we default to gcc8
which produces these warning

Signed-off-by: Joe Slater <joe.slater@windriver.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>

meta-gnome/recipes-gnome/metacity/metacity_3.28.0.bb

@@ -23,6 +23,11 @@ SRCREV = "c0d4b2fc0fcd6f2d3c37da935923f9e9ed5eb99f"
 
 EXTRA_OECONF += "--disable-xinerama"
 
+PACKAGECONFIG ?= ""
+
+# enable as neccessary until new warnings are dealt with
+PACKAGECONFIG[werror] = "--enable-Werror,--disable-Werror,,"
+
 do_configure_prepend() {
     cd ${S}
     aclocal --install || exit 1