sys_select tests: Check the signature of FD_*. * tests/test-select.c (FD_CLR, FD_ISSET, FD_SET, FD_ZERO): Move signature tests from here... * tests/test-sys_select.c (FD_CLR, FD_ISSET, FD_SET, FD_ZERO): ... to here. * modules/sys_select-tests (Files): Add tests/signature.h.