test: switch the unit tests to something resembling a test suite

The tests have inadvertent dependencies on each other so let's avoid
those by changing to a system that returns a null-terminated list of
test functions and our test runner iterates over those and forks off one
process per function.

test/misc.c

@@ -223,13 +223,17 @@ bswap_test(void)
     assert(result_64 == expect_64);
 }
 
-int
+const testfunc_t*
 misc_test(void)
 {
-    dix_version_compare();
-    dix_update_desktop_dimensions();
-    dix_request_size_checks();
-    bswap_test();
+    static const testfunc_t testfuncs[] = {
+        dix_version_compare,
+        dix_update_desktop_dimensions,
+        dix_request_size_checks,
+        bswap_test,
+        NULL,
+    };
+    return testfuncs;
 
     return 0;
 }