CHECK support for nullptr (fixes #341)

[sergiud]

This allows CHECK_NE(foo, nullptr) to compile and produces "nullptr" for the string representation of nullptr.

Finalizes #342

Closes #562 #341

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[drigz]

Thanks! Could you also add -DHAVE_CXX11_NULLPTR_T to common_copts in bazel/glog.bzl?

[sergiud]

@drigz In that case, ac_cv_cxx11_nullptr_t should also be set to 1 in common_config, correct?

[drigz]

@drigz In that case, ac_cv_cxx11_nullptr_t should also be set to 1 in common_config, correct?

Ah, I misread and thought that it was set to 1, sorry. Either approach is OK, in that case, but I have a slight preference for assuming a modern environment in the Bazel build: I think that people with weird environments use build systems with environment detection, and Bazel users are expecting the modern features.

[drigz]

Thanks!