verify tests: Fix spurious failure with parallel make. * gnulib-tool (func_emit_tests_Makefile_am): Emit initialization of EXTRA_PROGRAMS. * tests/test-verify.sh: Build test-verify-try.o, not test-verify.o. * tests/test-verify-try.c: New file. * modules/verify-tests (Files): Add it. (EXTRA_PROGRAMS): Add test-verify-try. (MOSTLYCLEANFILES): Update accordingly. Reported by Adam James Stewart <ajstewart@anl.gov>.