parallel-tests: Fix driver for nonempty executable extension. * automake.in (handle_tests): New substitution `%am__EXEEXT%', defined as 'FALSE' for non-generic rules, or if no programs are built at all. Otherwise, define it as configure conditional. * lib/am/check2.am [%am__EXEEXT%] (%EXT%$(EXEEXT).log): New conditional generic rule. * m4/init.m4: Hook an m4_provide of `_AM_COMPILER_EXEEXT' onto Autoconf's `_AC_COMPILER_EXEEXT' macro. (AM_INIT_AUTOMAKE): If `_AM_COMPILER_EXEEXT' has been provided at `AC_CONFIG_COMMANDS_PRE' time, then introduce a conditional `am__EXEEXT', defined to true iff `$EXEEXT' is nonempty. * tests/check5.test: Only match `_EXEEXT_[1-9]' here, to avoid false positives stemming from `@am__EXEEXT_TRUE@'. * NEWS: Update. Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>