tests: various minor tweakings, mostly related to AM_PROG_AR * tests/alloca.test: Adjust to new portability requirements due to the new AM_PROG_AR macro. * tests/discover.test: Likewise. * tests/libobj3.test: Likewise. * tests/pluseq7.test: Likewise. Also, make grepping of automake expected error message stricter. * tests/stdlib.test: Likewise, and extend the test a bit. * tests/parse.test (configure.in): Remove redundant call to AC_PROG_RANLIB. * tests/library2.test: Adjust to new portability requirements due to the new AM_PROG_AR macro. Also ... (configure.in): ... add call to AC_PROG_CC, to ensure automake really fails for the expected reason.