Configure conformance tests to build with C++11 (require GCC 4.8)

[skip ci]

conformance/Makefile.am

@@ -21,6 +21,7 @@ conformance_test_runner_SOURCES = conformance_test.cc conformance_test_runner.cc
                                   third_party/jsoncpp/jsoncpp.cpp
 nodist_conformance_test_runner_SOURCES = conformance.pb.cc
 conformance_test_runner_CPPFLAGS = -I$(top_srcdir)/src -I$(srcdir)
+conformance_test_runner_CXXFLAGS = -std=c++11
 # Explicit deps beacuse BUILT_SOURCES are only done before a "make all/check"
 # so a direct "make test_cpp" could fail if parallel enough.
 conformance_test_runner-conformance_test.$(OBJEXT): conformance.pb.h

travis.sh

@@ -11,6 +11,13 @@
 # For when some other test needs the C++ main build, including protoc and
 # libprotobuf.
 internal_build_cpp() {
+  # Install GCC 4.8 to replace the default GCC 4.6. We need 4.8 for more
+  # decent C++ 11 support in order to compile conformance tests.
+  sudo add-apt-repository ppa:ubuntu-toolchain-r/test -y
+  sudo apt-get update -qq
+  sudo apt-get install -qq g++-4.8
+  export CXX="g++-4.8" CC="gcc-4.8"
+
   ./autogen.sh
   ./configure
   make -j2