Support Protobuf v29 #1565

Job	Run time
clang-compile-with-bazel-all-options	16m 41s
clang-compile-with-boringssl	16m 54s
clang-compile-with-bazel	16m 14s
clang-compile-with-cmake	2m 50s
clang-compile-with-cmake-all-options	5m 19s
clang-compile-with-make	3m 23s
clang-compile-with-make-all-options	5m 17s
clang-unittest	15m 32s
gcc-compile-with-bazel	16m 46s
gcc-compile-with-bazel-all-options	17m 59s
gcc-compile-with-boringssl	17m 51s
gcc-compile-with-cmake	3m 24s
gcc-compile-with-cmake-all-options	5m 42s
gcc-compile-with-make	3m 25s
gcc-compile-with-make-all-options	5m 35s
	2h 32m 52s

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