Define NDEBUG when building 3rd party libraries.

We are not interested in asserts in 3rd party libraries so make them disappear
by defining NDEBUG when building them.

Closes #11155.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@61960 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

build/bakefiles/common.bkl

@@ -341,6 +341,12 @@
         -->
         <install-if>SHARED=='0'</install-if>
         <pic>$(substituteFromDict(SHARED, {'0':'off', '1':'on'}))</pic>
+
+        <!--
+            we don't want to have asserts in the 3rd party libraries code,
+            neither we nor wx users are interested in debugging them anyhow
+         -->
+        <define>NDEBUG</define>
     </template>