totalorder* tests: Verify also the function signatures. * tests/test-totalorder.h: New file, based on tests/test-totalorder.c. * tests/test-totalorder.c: Check the signature. Include test-totalorder.h for the rest. * tests/test-totalorderf.c: Include <config.h>, <math.h>. Check the signature. Include test-totalorder.h instead of test-totalorder.c. * tests/test-totalorderl.c: Likewise. * modules/totalorder-tests (Files): Add test-totalorder.h, signature.h. * modules/totalorderf-tests (Files): Add test-totalorder.h, signature.h. Remove test-totalorder.c. * modules/totalorderl-tests (Files): Likewise.