Merge commit 'flex-2.5.39^^'

This merges the same version of flex as we're using in prebuilts/misc
currently (but without the tiny branch that switched the version to
2.5.39 that weren't in the upstream master branch).

Also adds the METADATA, LICENSE, NOTICE, and MODULE_LICENSE_* files as
required.

Test: No Android.* files
Change-Id: If69488a1d78d5c7d4c1cc8955d55788bd5a639f2