Fix the lutin manual build process

2 jobs for master in 2 minutes and 48 seconds (queued for 2 seconds)
Name Stage Failure
build Build There is an unknown failure, please try again
mkdir objs
lutin -help > objs/lutin.tex
/bin/sh: 1: lutin: not found
Makefile:32: recipe for target 'objs/lutin.tex' failed
make[1]: Leaving directory '/builds/verimag/synchrone/lutin/doc/lutin-man'
make[1]: *** [objs/lutin.tex] Error 127
make: *** [man] Error 2
Makefile:35: recipe for target 'man' failed
ERROR: Job failed: exit code 1