cover CI hole which appears to be hiding a proc_macro bindgen bug (#1… #1584

Job	Run time
ASAN	9m 19s
Test Big Endian	10m 11s
macOS	15m 2s
UBSAN	7m 20s
Ubuntu 18.04 (Build: Debug, Compilers: gcc-6/g++-6, Shared Library: true)	10m 14s
Ubuntu 18.04 (Build: Debug, Compilers: clang-6.0/clang++-6.0, Shared Library: true)	9m 21s
Ubuntu 18.04 (Build: Debug, Compilers: clang-6.0/clang++-6.0, Shared Library: false)	9m 37s
Ubuntu 18.04 (Build: Release, Compilers: gcc-6/g++-6, Shared Library: true)	15m 41s
Ubuntu 18.04 (Build: Release, Compilers: gcc-6/g++-6, Shared Library: false)	15m 22s
Ubuntu 18.04 (Build: Release, Compilers: clang-6.0/clang++-6.0, Shared Library: true)	13m 58s
Ubuntu 18.04 (Build: Release, Compilers: clang-6.0/clang++-6.0, Shared Library: false)	14m 2s
Bazel	1m 59s
Windows 2019 (Generator: MinGW Makefiles, Shared Library: true)	21m 16s
Windows 2019 (Generator: MinGW Makefiles, Shared Library: false)	19m 40s
Windows 2019 (Generator: Visual Studio 16 2019, Shared Library: true)	8m 40s
Windows 2019 (Generator: Visual Studio 16 2019, Shared Library: false)	10m 56s
	3h 12m 38s

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