Add test_atomic_generalized to Makefile and Makefile.msft

Add test_atomic_generalized to Makefile and Makefile.msft

* src/Makefile.msft (test_atomic_generalized): New target (same as
test_atomic but with -D AO_PREFER_GENERALIZED).
* src/Makefile.msft (check): Add dependency on test_atomic_generalized;
run test_atomic_generalized.
* tests/Makefile.am (TESTS): Add test_atomic_generalized.
* tests/Makefile.am [HAVE_PTHREAD_H] (TEST): Add test_atomic_pthreads
instead of specifying all tests.
* tests/Makefile.am (test_atomic_generalized_SOURCES,
test_atomic_generalized_LDADD): Define (same as for test_atomic).
* tests/Makefile.am (test_atomic_generalized_CPPFLAGS): Define
specifying -D AO_PREFER_GENERALIZED.