libstdc++: Suppress -Waddress warning in tzdb.cc [PR108228]

For some tarets the weak symbol is always defined, so we get a warning
that its address is never null. The warning isn't useful in this case,
so suppress it.

libstdc++-v3/ChangeLog:

	PR libstdc++/108228
	* src/c++20/tzdb.cc (zoneinfo_dir): Add diagnostic pragma.

libstdc++-v3/src/c++20/tzdb.cc

@@ -1013,9 +1013,12 @@ namespace std::chrono
     string
     zoneinfo_dir()
     {
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Waddress"
       static const string dir = __gnu_cxx::zoneinfo_dir_override
 				  ? __gnu_cxx::zoneinfo_dir_override()
 				  : _GLIBCXX_ZONEINFO_DIR;
+#pragma GCC diagnostic pop
       return dir;
     }