Update Buildroot to version 2021.02

As Buildroot fixed [1] the glibc 2.33 compatibility issue, we should update
the Buildroot to reflect that change.

Link: [1] https://git.busybox.net/buildroot/commit/?id=f45925a951318e9e53bead80b363e004301adc6f
Signed-off-by: Mingyuan Xiang <xiang_my@outlook.com>
Acked-by: Jerome Forissier <jerome@forissier.org>
diff --git a/juno.xml b/juno.xml
index eacfc91..33928e3 100644
--- a/juno.xml
+++ b/juno.xml
@@ -19,7 +19,7 @@
         <project path="optee_examples"       name="linaro-swg/optee_examples.git" />
 
         <!-- Misc gits -->
-        <project path="buildroot"            name="buildroot/buildroot.git"               revision="refs/tags/2020.08" clone-depth="1" />
+        <project path="buildroot"            name="buildroot/buildroot.git"               revision="refs/tags/2021.02" clone-depth="1" />
         <project path="trusted-firmware-a"   name="TF-A/trusted-firmware-a.git"           revision="refs/tags/v2.2" clone-depth="1" remote="tfo" />
         <project path="u-boot"               name="u-boot/u-boot.git"                     revision="refs/tags/v2018.03" clone-depth="1" />
         <project path="vexpress-firmware"    name="arm/vexpress-firmware.git"             revision="670a8336738046ac910f4ed3746edc1b4ecf086c" remote="linaro"/>