package/squid: depends on current_exception

package/squid: depends on current_exception

Fixes build error

TextException.cc: In function 'std::ostream& CurrentException(std::ostream&)':
TextException.cc:64:9: error: 'current_exception' is not a member of 'std'
     if (std::current_exception()) {

using this defconfig

BR2_arm=y
BR2_TOOLCHAIN_EXTERNAL=y
BR2_TOOLCHAIN_EXTERNAL_CUSTOM=y
BR2_TOOLCHAIN_EXTERNAL_DOWNLOAD=y
BR2_TOOLCHAIN_EXTERNAL_URL="http://autobuild.buildroot.org/toolchains/tarballs/armv5-ctng-linux-gnueabi.tar.xz"
BR2_TOOLCHAIN_EXTERNAL_CUSTOM_PREFIX="armv5-ctng-linux-gnueabi"
BR2_TOOLCHAIN_EXTERNAL_GCC_4_8=y
BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_12=y
BR2_TOOLCHAIN_EXTERNAL_CUSTOM_GLIBC=y
BR2_TOOLCHAIN_EXTERNAL_CXX=y
BR2_PACKAGE_GNUTLS=y
BR2_PACKAGE_OPENSSL=y
BR2_PACKAGE_LIBKRB5=y

According to http://www.squid-cache.org/Versions/v4/RELEASENOTES.html#ss1.1
squid-4.2 depends on C++11, but adding -std=c++11 did not fix the build
error.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Tested-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
Reviewed-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>