doxygen @1.8.9.1: build fails with flex 2.6.0

[bl@…]

The build of doxygen fails on my freshly installed OSX El Capitan, given the following important log entry :

:info:build In file included from ../qtools/qshared.h:42:
:info:build ../qtools/qglobal.h:105:6: warning: "This version of Mac OS X is unsupported" [-W#warnings]
:info:build #    warning "This version of Mac OS X is unsupported"
:info:build      ^
:info:build vhdlcode.l:1618:2: error: "You seem to be using a version of flex newer than 2.5.4 but older than 2.5.33. These versions do NOT work with doxygen! Please use version <=2.5.4 or >=2.5.33 or expect things to be parsed wrongly!"
:info:build #error "You seem to be using a version of flex newer than 2.5.4 but older than 2.5.33. These versions do NOT work with doxygen! Please use version <=2.5.4 or >=2.5.33 or expect things to be parsed wrongly!"
:info:build  ^
:info:build 1 warning and 1 error generated.

So, this doxygen version don't know my OSX and there are some errors in the flex dependency.

Ps.: many other things works as expected om this installment.

[ryandesign (Ryan Carsten Schmidt)]

Duplicate of #49881.