Hi I have found the following compile error on openSUSE12.1 (uses FLTK1.3)
error in configure.ac - FLTK library not found -because test will not compile due to missing X11 libs -- fixed by adding
LIBS="`$FLTKCONFIG --use-images --ldflags` $LIBS"
AC_CHECK_LIB([fltk], [main], [ac_fltk="yes"], [ac_fltk="no"])
if test "x$ac_fltk" = "xno"; then
AC_MSG_ERROR([FLTK library not found.])