pdflatex documentation fails because of unicode character and other things

creating the latex documentation with make doc; cd bin/doc/latex; make fails:

Chapter 53.
(./md__home_castilma_.repo_ap_openage_doc_nyan_engine_types.tex [163]

! Package inputenc Error: Unicode char ⇒ (U+21D2)
(inputenc)                not set up for use with LaTeX.

See the inputenc package documentation for explanation.
Type  H <return>  for immediate help.
 ...                                              
                                                  
l.87 ... # WIP: how about checking (speed < 0) ⇒
                                                   instant before

somehow we (or doxygen) need to tell pdflatex not to choke on unicode characters. I haven't checked yet, what the option would be (maybe \usepackage[no_unicode_choke]{inputenc}) or how we would need to tell doxygen to write that options into the .tex files.
I wanted to see, if this was the only problem. It wasn't. I edited mentioned file and removed the troubling character. next error:

(./md__home_castilma_.repo_ap_openage_doc_reverse_engineering_unit_stats_unit_stats.
tex

! Package array Error:  Illegal pream-token (5): `c' used.

See the array package documentation for explanation.
Type  H <return>  for immediate help.
 ...                                              
                                                  
l.6 \begin{longtabu} spread 0pt [c]{*15{|X[-1]}|}

I'm confused by this. latex says check array package documentation for explanation, but longtabu is in from the tabu package. the longtabu doc mentions the c options and:

The tabu environment behaves mostly like tabular: the preamble is parsed by the macros in
array.sty and some measures are performed before printing. tabu improves tabular and array:

I don't exactly understand how latex packages work, but tabu seems to somehow change the behaviour of array which causes this error?
I changed the c to an r. Still the c is the problem. The question now is only, which c?

! Package array Error:  Illegal pream-token (5): `c' used.

See the array package documentation for explanation.
Type  H <return>  for immediate help.
 ...                                              
                                                  
l.6 \begin{longtabu} spread 0pt [r]{*15{|X[-1]}|}

So, what now? What is the direct cause of the problem? Who needs to fix his code?
EDIT: the c is not the problem, it is the 5 in {*15{...

Reproduce the failure with make doc; cd bin/doc/latex; make and inspect the generated .tex files named in the pdflatex output. Start with the Unicode inputenc error, then investigate the longtabu preamble in md__home_castilma_.repo_ap_openage_doc_reverse_engineering_unit_stats_unit_stats.tex. Done means the generated LaTeX documentation builds without these errors.