package/libodb-boost: fix build with gcc 11

Fixes:
 - No autobuilder failures yet

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
(cherry picked from commit 25d602a6a66bfecf17da0ca5edf589ace95e58db)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libodb-boost/libodb-boost.mk

@@ -12,5 +12,6 @@ LIBODB_BOOST_INSTALL_STAGING = YES
 LIBODB_BOOST_LICENSE = GPL-2.0
 LIBODB_BOOST_LICENSE_FILES = LICENSE
 LIBODB_BOOST_DEPENDENCIES = boost libodb
+LIBODB_BOOST_CONF_ENV = CXXFLAGS="$(TARGET_CXXFLAGS) -std=c++11"
 
 $(eval $(autotools-package))