Add 64-bit integers support to wxConfig

Serialize them to strings in wxFileConfig, just as we always did for
long, but use wxRegKey support for storing them directly to the registry
in wxRegConfig.

tests/config/fileconf.cpp

@@ -626,5 +626,18 @@ TEST_CASE("wxFileConfig::ReadFloat", "[fileconfig][config]")
     CHECK( f == -9876.5432f );
 }
 
+TEST_CASE("wxFileConfig::LongLong", "[fileconfig][config][longlong]")
+{
+    wxFileConfig fc("", "", "", "", 0); // Don't use any files.
+
+    // See comment near val64 definition in regconf.cpp.
+    const wxLongLong_t val = wxLL(0x8000000000000008);
+    REQUIRE( fc.Write("ll", val) );
+
+    wxLongLong_t ll;
+    REQUIRE( fc.Read("ll", &ll) );
+    CHECK( ll == val );
+}
+
 #endif // wxUSE_FILECONFIG