Add missing module header

Author: mborland

include/boost/decimal/detail/config.hpp

@@ -325,9 +325,15 @@ typedef unsigned __int128 uint128_t;
 #  endif
 #endif
 
+// Since we should not be able to pull these in from the STL in module mode define them ourselves
+// This is also low risk since they are not supposed to be exported
 #ifdef BOOST_DECIMAL_BUILD_MODULE
-#  define UINT64_C(x) (x ## ULL)
-#  define UINT32_C(x) (x ## UL)
+#  ifndef UINT64_C
+#    define UINT64_C(x) (x ## ULL)
+#  endif
+#  ifndef UINT32_C
+#    define UINT32_C(x) (x ## UL)
+#  endif
 #endif
 
 #endif // BOOST_DECIMAL_DETAIL_CONFIG_HPP

modules/decimal.cxx

@@ -29,6 +29,7 @@ module;
 #include <system_error>
 #include <complex>
 #include <compare>
+#include <charconv>
 
 // <stdfloat> is a C++23 feature that is not everywhere yet
 #if __has_include(<stdfloat>)