Ha, hm. Wrong error log ...
(the kind of stupid mistake I'm good at)
gcc ccnet.o cd_file.o cd_sys.o cdda_mp3.o cpu_68k.o cpu_sh2.o cpu_z80.o lc89510.o m68kd.o pcm.o port.o psg.o sh2.o sh2d.o timer.o unzip.o wave.o ym2612.o z80dis.o cd_aspi.o debug.o g_ddraw.o g_dinput_dummy.o g_dsound_dummy.o g_main_dummy.o gens.o movie.o ggenie.o rom.o save.o scrshot.o blit.o gfx_cd.o io.o mem_m68k.o mem_s68k.o mem_sh2.o mem_z80.o misc.o pwm.o sh2a.o vdp_32x.o vdp_io.o vdp_rend.o z80.o ram_search.o mp3_dec/dct64_i386.o mp3_dec/layer3.o mp3_dec/common.o mp3_dec/decode_i386.o mp3_dec/interface.o mp3_dec/tabinit.o ../Starscream/Main68k/main68k.o ../Starscream/Sub68k/sub68k.o nesvideos-piece.o -lm `sdl-config --libs` -lz -lstdc++ -lreadline -s -o gens
g_main_dummy.o: In function `Set_Render':
/sources/gens_linux/gens/g_main_dummy.cpp:530: undefined reference to `XConfigureWindow'
g_main_dummy.o: In function `update_ui_events()':
/sources/gens_linux/gens/g_main_dummy.cpp:782: undefined reference to `XLowerWindow'
/sources/gens_linux/gens/g_main_dummy.cpp:782: undefined reference to `XSetInputFocus'
/sources/gens_linux/gens/g_main_dummy.cpp:786: undefined reference to `XRaiseWindow'
[trimmed, there are about a dozen more similar lines]
/sources/gens_linux/gens/g_main_dummy.cpp:1233: undefined reference to `XSetInputFocus'
g_main_dummy.o: In function `main':
/sources/gens_linux/gens/g_main_dummy.cpp:1512: undefined reference to `XConfigureWindow'
collect2: ld returned 1 exit status
make: *** [all] Error 1