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

[LEDE Bugs]

A new Flyspray task has been opened.  Details are below. 

User who did this - Michael Marley (mamarley) 

Attached to Project - LEDE Project
Summary - Commit 8040420b006a744ad65d4f2bedf5682140df1f42 (tools/flex: update to 2.6.3) breaks Unbound build
Task Type - Bug Report
Category - Base system
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - Medium
Priority - Very Low
Reported Version - Trunk
Due in Version - Undecided
Due Date - Undecided
Details - After https://git.lede-project.org/?p=source.git;a=commit;h=8040420b006a744ad65d4f2bedf5682140df1f42, Unbound is FTBFS with the following error message:

/tmp/ccjylqAI.ltrans0.ltrans.o: In function `main':
:(.text.startup+0x2257): undefined reference to `ub_c_lex_destroy'
/home/michael/Source/lede/myrouter/build_dir/target-x86_64_musl/unbound-1.6.2/.libs/libunbound.so: undefined reference to `ub_c_in'
/home/michael/Source/lede/myrouter/build_dir/target-x86_64_musl/unbound-1.6.2/.libs/libunbound.so: undefined reference to `ub_c_lex'
/home/michael/Source/lede/myrouter/build_dir/target-x86_64_musl/unbound-1.6.2/.libs/libunbound.so: undefined reference to `yywrap'
collect2: error: ld returned 1 exit status
Makefile:318: recipe for target 'unbound' failed
make[4]: *** [unbound] Error 1

Reverting the commit allows Unbound to build successfully again.

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