> Best delete your build directory and compile from scratch.

Done, but the result is the same :-( I have created/downloaded the branch today the first time. First lines of the output of ./compile.sh:

-- The C compiler identification is GNU 7.1.1                                                                                                                   
-- The CXX compiler identification is GNU 7.1.1                                                                                                                 
-- Check for working C compiler: /usr/bin/cc                                                                                                                    
-- Check for working C compiler: /usr/bin/cc -- works                                                                                                           
-- Detecting C compiler ABI info                                                                                                                                
-- Detecting C compiler ABI info - done                                                                                                                         
-- Detecting C compile features                                                                                                                                 
-- Detecting C compile features - done                                                                                                                          
-- Check for working CXX compiler: /usr/bin/c++                                                                                                                 
-- Check for working CXX compiler: /usr/bin/c++ -- works                                                                                                        
-- Detecting CXX compiler ABI info                                                                                                                              
-- Detecting CXX compiler ABI info - done                                                                                                                       
-- Detecting CXX compile features                                                                                                                               
-- Detecting CXX compile features - done                                                                                                                        
-- Boost version: 1.64.0                                                                                                                                        
-- Found the following Boost libraries:                                                                                                                         
--   unit_test_framework                                                                                                                                        
--   regex                                                                                                                                                      
-- Found PythonInterp: /usr/bin/python (found version "3.6.1")                                                                                                  
-- Found Gettext: /usr/bin/msgmerge (found version "0.19.8.1")                                                                                                  
-- Found OpenGL: /usr/lib/libGL.so                                                                                                                              
-- Found ZLIB: /usr/lib/libz.so (found version "1.2.11")                                                                                                        
-- Found PNG: /usr/lib/libpng.so (found version "1.6.29")                                                                                                       
-- SDL2_INCLUDE_DIR is /usr/include/SDL2
-- SDL2MAIN_LIBRARY is /usr/lib/libSDL2main.a
-- Looking for pthread.h
-- Looking for pthread.h - found
-- Looking for pthread_create
-- Looking for pthread_create - not found
-- Looking for pthread_create in pthreads
-- Looking for pthread_create in pthreads - not found
-- Looking for pthread_create in pthread
-- Looking for pthread_create in pthread - found
-- Found Threads: TRUE  
-- Found SDL2_image: /usr/lib/libSDL2_image.so  
-- Found SDL2_mixer: /usr/lib/libSDL2_mixer.so (found version "2.0.1") 
-- Found SDL2_net: /usr/lib/libSDL2_net.so (found version "2.0.1") 
-- Found SDL2_ttf: /usr/lib/libSDL2_ttf.so (found version "2.0.14") 
-- Found ICU: /usr/lib/libicuuc.so (found version "59.1.0") 
-- Version of Widelands Build is bzr8377[bug-794407-soldier-stats](Debug)
-- Found Doxygen: /usr/bin/doxygen (found version "1.8.13") 
-- Configuring done
-- Generating done
-- Build files have been written to: /home/kaputtnik/Quellcode/widelands-repo/bug-794407-soldier-stats/build
Scanning dependencies of target BzrRevision
-- Version of Widelands Build is bzr8377[bug-794407-soldier-stats](Debug)