libc++abi: Don't print debugging messages to stdout

[ed]

Summary

There is some debugging code in cxa_demangle.cpp that prints messages on stdout. In general this is not safe, as the program itself may use stdout to write its output. Change this code to write to stderr.

Testing has revealed that this code is actually not reachable. Maybe it would make sense to remove it instead?

[ed]

Adding another reviewer.

src/cxa_demangle.cpp

 void
 print_stack(const C& db)
 {
-    printf("---------\n");
-    printf("names:\n");
+    fprintf(stderr, "---------\n");
+    fprintf(stderr, "names:\n");
     for (auto& s : db.names)
-        printf("{%s#%s}\n", s.first.c_str(), s.second.c_str());
+        fprintf(stderr, "{%s#%s}\n", s.first.c_str(), s.second.c_str());
     int i = -1;
-    printf("subs:\n");
+    fprintf(stderr, "subs:\n");
     for (auto& v : db.subs)
     {
         if (i >= 0)
-            printf("S%i_ = {", i);
+            fprintf(stderr, "S%i_ = {", i);
         else
-            printf("S_  = {");
+            fprintf(stderr, "S_  = {");
         for (auto& s : v)
-            printf("{%s#%s}", s.first.c_str(), s.second.c_str());
-        printf("}\n");
+            fprintf(stderr, "{%s#%s}", s.first.c_str(), s.second.c_str());
+        fprintf(stderr, "}\n");
         ++i;
     }
-    printf("template_param:\n");
+    fprintf(stderr, "template_param:\n");
     for (auto& t : db.template_param)
     {
-        printf("--\n");
+        fprintf(stderr, "--\n");
         i = -1;
         for (auto& v : t)
         {
             if (i >= 0)
-                printf("T%i_ = {", i);
+                fprintf(stderr, "T%i_ = {", i);
             else
-                printf("T_  = {");
+                fprintf(stderr, "T_  = {");
             for (auto& s : v)
-                printf("{%s#%s}", s.first.c_str(), s.second.c_str());
-            printf("}\n");
+                fprintf(stderr, "{%s#%s}", s.first.c_str(), s.second.c_str());
+            fprintf(stderr, "}\n");
             ++i;
         }
     }
-    printf("---------\n\n");
+    fprintf(stderr, "---------\n\n");
 }
 
 template <class C>

 void
 print_state(const char* msg, const char* first, const char* last, const C& db)
 {
-    printf("%s: ", msg);
+    fprintf(stderr, "%s: ", msg);
     for (; first != last; ++first)
-        printf("%c", *first);
-    printf("\n");
+        fprintf(stderr, "%c", *first);
+    fprintf(stderr, "\n");
     print_stack(db);
 }