treewide: retain sections to prevent linker garbage collection

The linker may remove sections that are actually used when
"--gc-sections" and "-z start-stop-gc" is set. Add the `retain`
attribute to prevent that.

Furthermore, fix the alignment for `pwtest_suite_decl` objects.

See: #2292
See: https://lld.llvm.org/ELF/start-stop-gc.html
See: https://github.com/systemd/systemd/issues/21847
See: https://github.com/systemd/systemd/pull/21855

src/modules/module-protocol-pulse/module.h

@@ -47,6 +47,7 @@ struct module_info {
 
 #define DEFINE_MODULE_INFO(name)					\
 	__attribute__((used))						\
+	__attribute__((retain))						\
 	__attribute__((section("pw_mod_pulse_modules")))		\
 	__attribute__((aligned(__alignof__(struct module_info))))	\
 	const struct module_info name