libraries/msgpack-c: Use the C++11 standard.

gcc >= 11.x defaults to -std=gnu++17 and it breaks the build
in this case

Signed-off-by: Matteo Bernardini <ponce@slackbuilds.org>

Signed-off-by: Willy Sudiarto Raharjo <willysr@slackbuilds.org>

libraries/msgpack-c/msgpack-c.SlackBuild

@@ -85,7 +85,7 @@ mkdir -p build
 cd build
   cmake \
     -DCMAKE_C_FLAGS:STRING="$SLKCFLAGS" \
-    -DCMAKE_CXX_FLAGS:STRING="$SLKCFLAGS" \
+    -DCMAKE_CXX_FLAGS:STRING="$SLKCFLAGS -std=c++11" \
     -DCMAKE_BUILD_TYPE=Release \
     -DCMAKE_INSTALL_PREFIX=/usr \
     -DCMAKE_INSTALL_LIBDIR=/usr/lib${LIBDIRSUFFIX} \