u-boot-envtools: fix building with glibc

tools/env/fw_env.c misses to include stdint.h.
Apparently musl doesn't mind and includes this header by default,
but glibc does not and causes the build to fail.

Signed-off-by: Josua Mayer <josua.mayer97@gmail.com>

package/boot/uboot-envtools/patches/400-u-boot-2015.10-stdint.patch

@@ -0,0 +1,13 @@
+diff -Naur u-boot-2015.10.orig/tools/env/fw_env.c u-boot-2015.10/tools/env/fw_env.c
+--- u-boot-2015.10.orig/tools/env/fw_env.c	2016-06-24 12:42:31.152391850 +0200
++++ u-boot-2015.10/tools/env/fw_env.c	2016-06-24 12:42:59.080391754 +0200
+@@ -21,7 +21,8 @@
+ #include <sys/types.h>
+ #include <sys/ioctl.h>
+ #include <sys/stat.h>
+-#include <unistd.h>
++#include <unistd.h>
++#include <stdint.h>
+ 
+ #ifdef MTD_OLD
+ # include <stdint.h>