Improve and extend tests `asm*.test'. * tests/asm.test: Use configure.in stub generated by ./defs, and avoid obsoleted autoconf constructs. Make grepping of Automake stderr stricter. Do not create useless source file. Improve verbose messages. Minor cosmetic changes. Tell to keep it in sync with other sister tests asm*.test. * tests/asm2.test: Likewise. * tests/asm3.test: Likewise.