[Buildroot] [git commit branch/2021.02.x] package/ibrdtn: fix build with gcc 11

[Peter Korsgaard]

commit: https://git.buildroot.net/buildroot/commit/?id=58682a273927b785f4b6e15eacdbdd216cb38cfe
branch: https://git.buildroot.net/buildroot/commit/?id=refs/heads/2021.02.x

Fix the following build failure with gcc 11:

In file included from ../../ibrdtn/data/PrimaryBlock.h:30,
                 from ../../ibrdtn/data/Serializer.h:27,
                 from ../../ibrdtn/data/Block.h:29,
                 from ../../ibrdtn/data/Bundle.h:27,
                 from ../../ibrdtn/api/Client.h:26,
                 from Client.cpp:22:
/tmp/instance-0/output-1/host/bin/../arm-buildroot-linux-gnueabihf/sysroot/usr/include/ibrcommon-1.0/ibrcommon/thread/Mutex.h:43:40: error: ISO C++17 does not allow dynamic exception specifications
   43 |                 virtual void trylock() throw (MutexException) = 0;
      |                                        ^~~~~

Fixes:
 - http://autobuild.buildroot.org/results/c2d9033c68b5c1407d2cf87b98dff61958b8e7b6

Signed-off-by: Fabrice Fontaine <fontaine.fabrice at gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni at bootlin.com>
(cherry picked from commit 581687e34b067c8dac06335dbae640a23b9e505c)
Signed-off-by: Peter Korsgaard <peter at korsgaard.com>
---
 package/ibrdtn/ibrdtn.mk | 1 +
 1 file changed, 1 insertion(+)

diff --git a/package/ibrdtn/ibrdtn.mk b/package/ibrdtn/ibrdtn.mk
index 3f805c4024..99ff92d442 100644
--- a/package/ibrdtn/ibrdtn.mk
+++ b/package/ibrdtn/ibrdtn.mk
@@ -10,6 +10,7 @@ IBRDTN_INSTALL_STAGING = YES
 IBRDTN_LICENSE = Apache-2.0
 IBRDTN_LICENSE_FILES = COPYING
 IBRDTN_DEPENDENCIES = ibrcommon host-pkgconf
+IBRDTN_CONF_ENV = CXXFLAGS="$(TARGET_CXXFLAGS) -std=c++11"
 
 ifeq ($(BR2_PACKAGE_ZLIB),y)
 IBRDTN_CONF_OPTS += --with-compression