Add support for multiple M_LET on the same line

without warning about shadow variables.

example/ex-mph.c

@@ -234,9 +234,7 @@ test(array_seed_t seed, array_value_t value, dict_mph_t dict)
 
 int main(int argc, const char *argv[])
 {
-  M_LET(arr, array_string_t)
-    M_LET(dict, dict_mph_t)
-    M_LET(seed, array_seed_t)
+  M_LET(arr, array_string_t) M_LET(dict, dict_mph_t) M_LET(seed, array_seed_t)
     M_LET(value, array_value_t) {
     const char *filename = (argc > 1) ? argv[1] :"/usr/share/dict/words";
     dict_read_from_file(dict, arr, filename);

m-core.h

@@ -1959,8 +1959,8 @@ m_core_hash (const void *str, size_t length)
    Last argument can be the oplist or the type itself if a global
    oplist has been recorded for this type.
  */
-#define M_LET(...)                                                      \
-  M_ID(M_LETI1 M_INVERT( __VA_ARGS__, M_C(local_cont_, __LINE__) ))
+#define M_LET(a, ...)                                                   \
+  M_ID(M_LETI1 M_INVERT(a, __VA_ARGS__, M_C3(local_cont_, a, __LINE__) ))
 
 #define M_LETI1(cont, oplist, ...)                                      \
   M_LETI2(cont, M_GLOBAL_OPLIST(oplist), __VA_ARGS__)