Do not require literal message ids in Atlas

In >=wxWidgets-3.3 there is a new static check for literal message
ids[1] so that xgettext would reliable work to extract strings to
translate. As we don't translate Atlas at all nor use xgettext just
disable the check to allow building against >=wxWidgets-3.3.

[1] https://wxwidgets.org/help/msgid-literals/

Signed-off-by: Ralph Sennhauser <ralph.sennhauser@gmail.com>

build/premake/extern_libs5.lua

@@ -734,6 +734,7 @@ extern_lib_defs = {
 				-- so we have to use wxwidgets' own config tool
 				pkgconfig.add_includes(nil, wx_config_path(), "--unicode=yes --cxxflags")
 			end
+			defines({ "wxNO_REQUIRE_LITERAL_MSGIDS" })
 		end,
 		link_settings = function()
 			if os.istarget("windows") then