Fixed a build error for single-threaded Linux

.gitignore

@@ -0,0 +1 @@
+build

src/utils/os_unix.c

@@ -823,9 +823,9 @@ int os_exec(const char *program, const char *arg, int wait_completion)
 	pid_t pid;
 	int pid_status;
 
-	pid = fork();
+	pid = vfork();
 	if (pid < 0) {
-		perror("fork");
+		perror("vfork");
 		return -1;
 	}