fixed a few more small bugs reported by Stanislav Brabec

fixed a few more small bugs reported by Stanislav Brabec

- A function uses a 'return;' statement, but has actually a value to
return, like an integer ('return 42;') or similar: xboard voidreturn
xengineoutput.c:766, 782

- Program returns random data in a function at xengineoutput.c:602

- With a new toolchain, AM_LDFLAGS cannot contain libraries. Linker
ignores them. Fix is attached.

- ToDo: Convenient name in most projects is TODO (autotools package it
automatically).