parallel-tests: automake error our on invalid TEST_EXTENSIONS This change fixes automake bug#9400. * automake.in (handle_tests): Bail out if a suffix specified in TEST_EXTENSIONS would produce an invalid `xxx_LOG_COMPILER' variable or an invalid suffix rule. Before this change, automake would have issued a confusing error messages (about invalid or non-POSIX variables being defined), and in some situations would have even produced a broken `Makefile.in' file. ($TEST_EXTENSION_PATTERN): New helper variable. * doc/automake.texi (Simple Tests using parallel-tests): Document the limitations on TEST_EXTENSIONS explicitly. * NEWS: Update. * tests/test-extensions.test: New test. * tests/Makefile.am (TESTS): Update.