If building with CURLDEBUG, sprintf() is defined away. So use curl_msprintf()

and not sprintf().

src/writeenv.c

@@ -94,7 +94,7 @@ void ourWriteEnv(CURL *curl)
 
     case writeenv_LONG:
       if (curl_easy_getinfo(curl, variables[i].id, &longinfo) == CURLE_OK) {
-        sprintf(numtext, "%5ld", longinfo);
+        curl_msprintf(numtext, "%5ld", longinfo);
         internalSetEnv(variables[i].name, numtext);
       }
       else
@@ -102,7 +102,7 @@ void ourWriteEnv(CURL *curl)
       break;
     case writeenv_DOUBLE:
       if (curl_easy_getinfo(curl, variables[i].id, &doubleinfo) == CURLE_OK) {
-        sprintf(numtext, "%6.2f", doubleinfo);
+        curl_msprintf(numtext, "%6.2f", doubleinfo);
         internalSetEnv(variables[i].name, numtext);
       }
       else