squid: requires C++11 toolchain

squid: requires C++11 toolchain

The squid changelog for version 4.0.1 mentions that "C++11 compiler
support is now mandatory". The code uses the std::map::emplace method
that gcc before 4.8 does not support.

Also fixes:
http://autobuild.buildroot.net/results/370/37093f8d3395850b2db5ed645f60d1c2df92768d/
http://autobuild.buildroot.net/results/921/92117726e7b4ede08dcc0e4fd1a85171fd17aeb8/
http://autobuild.buildroot.net/results/e67/e679ef90219c5e8f9c94ddcd7d3f9582f79ef751/

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>