LM (Linux): try fixing LightDM version detection

src/common/processing_linux.c

@@ -47,3 +47,45 @@ const char* ffProcessAppendStdOut(FFstrbuf* buffer, char* const argv[])
 
     return NULL;
 }
+
+const char* ffProcessAppendStdErr(FFstrbuf* buffer, char* const argv[])
+{
+    int pipes[2];
+
+    if(pipe(pipes) == -1)
+        return "pipe() failed";
+
+    pid_t childPid = fork();
+    if(childPid == -1)
+        return "fork() failed";
+
+    //Child
+    if(childPid == 0)
+    {
+        dup2(pipes[1], STDERR_FILENO);
+        close(pipes[0]);
+        close(pipes[1]);
+        close(STDOUT_FILENO);
+        execvp(argv[0], argv);
+        exit(901);
+    }
+
+    //Parent
+    close(pipes[1]);
+
+    int FF_AUTO_CLOSE_FD childPipeFd = pipes[0];
+    int status = -1;
+    if(waitpid(childPid, &status, 0) < 0)
+        return "waitpid(childPid, &status, 0) failed";
+
+    if (!WIFEXITED(status))
+        return "WIFEXITED(status) == false";
+
+    if(WEXITSTATUS(status) == 901)
+        return "WEXITSTATUS(status) == 901 ( execvp failed )";
+
+    if(!ffAppendFDBuffer(childPipeFd, buffer))
+        return "ffAppendFDBuffer(childPipeFd, buffer) failed";
+
+    return NULL;
+}