to old compilers that default to < C++11.  (Explicitly passing CXXFLAGS_CXX11
into ExternalProject_breakpad wouldn't work well for now, as it would cause
-Wregister error with -std=c++17 at
workdir/UnpackedTarball/breakpad/src/common/dwarf/dwarf2reader.cc:878:43.)

Change-Id: I1d04e0f05e36e2f9622991fb477f430a062fee0b