Update buildroot to 2021.11

Update buildroot to version 2021.11. Fixes a build error with
qemu_v8.xml and "make XEN_BOOT=y check" (host compiler is
"gcc (Ubuntu 11.2.0-7ubuntu2) 11.2.0"):

 ../glib/gspawn.c: In function ‘safe_closefrom’:
 ../glib/gspawn.c:1497:7: error: too few arguments to function ‘close_range’
  1497 |   if (close_range (lowfd, G_MAXUINT) != 0 && errno == ENOSYS)
       |       ^~~~~~~~~~~
 In file included from /usr/include/unistd.h:1204,
                  from /usr/include/x86_64-linux-gnu/bits/sigstksz.h:24,
                  from /usr/include/signal.h:328,
                  from /usr/include/x86_64-linux-gnu/sys/wait.h:36,
                  from ../glib/gspawn.c:25:
 /usr/include/x86_64-linux-gnu/bits/unistd_ext.h:56:12: note: declared here
    56 | extern int close_range (unsigned int __fd, unsigned int __max_fd,
       |            ^~~~~~~~~~~

Signed-off-by: Jerome Forissier <jerome@forissier.org>
Change-Id: Ic07aaa68b14dfcb46799a626edd23b1783c76097
Reviewed-by: Joakim Bech <joakim.bech@linaro.org>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/poplar.xml b/poplar.xml
index 49d91e3..cbb9514 100644
--- a/poplar.xml
+++ b/poplar.xml
@@ -24,6 +24,6 @@
         <project path="u-boot"               name="u-boot/u-boot.git"                     revision="refs/tags/v2021.07" clone-depth="1" remote="denx" />
 
         <!-- Misc gits -->
-        <project path="buildroot"            name="buildroot/buildroot.git"               revision="refs/tags/2021.08" clone-depth="1" />
+        <project path="buildroot"            name="buildroot/buildroot.git"               revision="refs/tags/2021.11" 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" />
 </manifest>