Building no-warning-test fails with -Og in CXXFLAGS

[Peter-Levine]

When building with GCC, inclusion of -Og in CXXFLAGS causes make check to fail with errors such as:

In file included from google/protobuf/compiler/cpp/cpp_test_bad_identifiers.pb.cc:5:0:
./google/protobuf/compiler/cpp/cpp_test_bad_identifiers.pb.h: In member function ‘virtual bool protobuf_unittest::TestConflictingEnumNames::MergePartialFromCodedStream(google::protobuf::io::CodedInputStream*)’:
./google/protobuf/compiler/cpp/cpp_test_bad_identifiers.pb.h:3798:21: error: ‘value’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
   conflicting_enum_ = value;
   ~~~~~~~~~~~~~~~~~~^~~~~~~
google/protobuf/compiler/cpp/cpp_test_bad_identifiers.pb.cc:6765:15: note: ‘value’ was declared here
           int value;
               ^~~~~

This appears to be related to Bug 58455 - spurious "may be used uninitialized" warning with -Og and Bug 42145 - bogus "may be used uninitialized" (a || b converted to a|b). As part of protobuf gets built with -Werror, such spurious warnings become fatal.

Tested with protobuf-3.3.0 using GCC-5.4.0 and GCC-6.4.0.

See also Bug 618150 - dev-libs/protobuf-3.3.0 - error: 'value' may be used uninitialized in this function [-Werror=maybe-uninitialized]