[FS#809] Commit 8040420b006a744ad65d4f2bedf5682140df1f42 (tools/flex: update to 2.6.3) breaks Unbound build

[LEDE Bugs]

The following task has a new comment added:

FS#809 - Commit 8040420b006a744ad65d4f2bedf5682140df1f42 (tools/flex: update to 2.6.3) breaks Unbound build
User who did this - Eric Luehrsen (EricLuehrsen)

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Unbound tracker: https://nlnetlabs.nl/bugs-script/show_bug.cgi?id=1223 
Flex tracker: https://github.com/westes/flex/issues/162 
Discovered Bug in Flex 2.6.3 - 2017-JAN-17
Proposed Fix in Flex Master - 2017-JAN-23
Released Fix in Flex 2.6.4 - 2017-MAY-06

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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=809#comment2672