fix MSVC C++20 module build error C2872, C2039, C2873 on 'literals'

Fixed the errors from Visual Studio 2022 version 17.13.5 Compiler Version 19.43.34809 that appeared when building "tomlplusplus_modules", saying:

    src\modules\tomlpp.cppm(22,21): error C2872: 'literals': ambiguous symbol
        src\modules\tomlpp.cppm(21,22):
        could be 'toml::literals'
        include\toml++\impl\parser.hpp(322,19):
        or       'toml::v3::literals'
    src\modules\tomlpp.cppm(22,31): error C2039: '""_toml': is not a member of 'toml::literals'
        src\modules\tomlpp.cppm(21,22):
        see declaration of 'toml::literals'
    src\modules\tomlpp.cppm(22,9): error C2873: '""_toml': symbol cannot be used in a using-declaration
    src\modules\tomlpp.cppm(23,21): error C2872: 'literals': ambiguous symbol
        src\modules\tomlpp.cppm(21,22):
        could be 'toml::literals'
        include\toml++\impl\parser.hpp(322,19):
        or       'toml::v3::literals'
    src\modules\tomlpp.cppm(23,31): error C2039: '""_tpath': is not a member of 'toml::literals'
        src\modules\tomlpp.cppm(21,22):
        see declaration of 'toml::literals'
    src\modules\tomlpp.cppm(23,9): error C2873: '""_tpath': symbol cannot be used in a using-declaration

Author: N-Dekker

src/modules/tomlpp.cppm

@@ -5,6 +5,7 @@
 
 module;
 
+#define TOML_UNDEF_MACROS 0
 #include <toml++/toml.hpp>
 
 export module tomlplusplus;
@@ -19,8 +20,8 @@ export namespace toml {
      * @brief The toml++ namespace toml::literals::
      */
     inline namespace literals {
-        using toml::literals::operator""_toml;
-        using toml::literals::operator""_tpath;
+        using TOML_NAMESPACE::literals::operator""_toml;
+        using TOML_NAMESPACE::literals::operator""_tpath;
     }
 
     using toml::array;