Taking a hint from William Pitcock's firefox APKBUILD 
features.h causes problems when pulling in system headers - we don't need it

diff --git a/mozilla/config/system-headers b/mozilla/config/system-headers
index 403fa8d..182e928 100644
--- a/mozilla/config/system-headers
+++ b/mozilla/config/system-headers
@@ -420,7 +420,6 @@ execinfo.h
 extras.h
 fabdef.h
 fcntl.h
-features.h
 fibdef.h
 File.h
 filehdr.h