fs.c: Fix implicit declaration of function 'mkstemp'

system/core/libcutils/fs.c: In function 'fs_write_atomic_int':
system/core/libcutils/fs.c:109:5: warning: implicit declaration of function 'mkstemp' [-Wimplicit-function-declaration]

Change-Id: I337ecb818f85e20b058f782df45987acf2e9d6c1
diff --git a/libcutils/fs.c b/libcutils/fs.c
index 1226d44..116526d 100644
--- a/libcutils/fs.c
+++ b/libcutils/fs.c
@@ -26,6 +26,7 @@
 #include <errno.h>
 #include <string.h>
 #include <limits.h>
+#include <stdlib.h>
 
 #define ALL_PERMS (S_ISUID | S_ISGID | S_ISVTX | S_IRWXU | S_IRWXG | S_IRWXO)
 #define BUF_SIZE 64