fix module compilation with clang on windows when std module is disabled

module/argparse.cppm

@@ -29,15 +29,22 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE  OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
 */
 
+module;
+
+#ifndef ARGPARSE_MODULE_USE_STD_MODULE
+#include <argparse/argparse.hpp>
+#endif 
+
 export module argparse;
 
 #ifdef ARGPARSE_MODULE_USE_STD_MODULE
 import std;
-#endif
 
 extern "C++" {
 #include <argparse/argparse.hpp>
 }
+#endif
+
 
 export namespace argparse {
     using argparse::nargs_pattern;

xmake.lua

@@ -4,6 +4,7 @@ set_project("argparse")
 set_version("2.9.0", { build = "%Y%m%d%H%M" })
 
 option("enable_module")
+option("enable_std_import", { defines = "ARGPARSE_MODULE_USE_STD_MODULE" })
 option("enable_tests")
 option("enable_samples")
 
@@ -28,7 +29,9 @@ target("argparse", function()
     if get_config("enable_module") then
         set_languages("c++20")
         set_kind("static") -- static atm because of a XMake bug, headeronly doesn't generate package module metadata
-    else
+    end
+
+    add_options("enable_std_import")
 
     add_includedirs("include", { public = true })
     add_headerfiles("include/argparse/argparse.hpp")