Add /app/lib to ld.so.conf

When using the SDK as a replacment for FD.o/GNOME/KDE upstream's to build
with flatpak-builder, libraries will be built into /app/lib rather than in
/app/lib64 as in Fedora builds.

defaults.json.in

@@ -3,5 +3,5 @@
   "cflags": "%{build_cflags}",
   "cxxflags": "%{build_cxxflags}",
   "cppflags": "",
-  "ldflags": "-L/app/%{_lib} %{build_ldflags}"
+  "ldflags": "-L/app/lib %{build_ldflags}"
 }

flatpak-runtime-config.spec

@@ -72,6 +72,9 @@ include /run/flatpak/ld.so.conf.d/app-*.conf
 include /app/etc/ld.so.conf
 include /app/etc/ld.so.conf.d/*.conf
 /app/%{_lib}
+%if "%{_lib}" != "lib"
+/app/lib
+%endif
 include /run/flatpak/ld.so.conf.d/runtime-*.conf
 _EOF