don't include in extern c #2468

Job	Run time
clang-sanitizers (,thread)	2m 27s
downstream	46m 57s
clang-sanitizers (,address,undefined)	1m 50s
Cross Compile linux-armv6	1m 56s
Cross Compile linux-armv7	1m 57s
Cross Compile linux-arm64	1m 46s
freebsd	9m 36s
linux-compat (manylinux1-x64)	1m 5s
Cross Compile android-armv7	2m 13s
linux-compat (manylinux1-x86)	1m 10s
linux-compiler-compat (clang-3)	1m 51s
linux-no-cpu-extensions	1m 40s
linux-compat (manylinux2014-x64)	1m 21s
linux-compiler-compat (clang-6)	6m 0s
linux-compat (manylinux2014-x86)	1m 16s
linux-compiler-compat (clang-8)	6m 27s
linux-shared-libs	1m 30s
linux-compiler-compat (clang-9)	6m 8s
linux-compiler-compat (clang-10)	1m 45s
linux-compat (raspbian-bullseye)	6m 53s
linux-compat (fedora-34-x64)	1m 46s
linux-compiler-compat (clang-11)	1m 48s
macos	1m 26s
linux-compiler-compat (gcc-4.8)	1m 29s
linux-compat (opensuse-leap)	1m 25s
linux-compiler-compat (gcc-5)	1m 41s
linux-compat (rhel8-x64)	1m 9s
macos-no-cpu-extensions	1m 17s
linux-compiler-compat (gcc-6)	1m 38s
linux-compat (al2-x64)	1m 9s
linux-compiler-compat (gcc-7)	1m 43s
linux-compiler-compat (gcc-8)	1m 45s
macos-x64	2m 41s
linux-compiler-compat (gcc-11)	1m 54s
openbsd	12m 2s
windows	2m 28s
windows-app-verifier	22m 55s
windows-shared-libs	2m 41s
windows-no-cpu-extensions	2m 38s
windows-vc14 (x86)	2m 17s
windows-vc15 (x86)	3m 26s
windows-vc16 (x86)	2m 57s
windows-vc14 (x64)	2m 39s
windows-vc15 (x64)	2m 43s
windows-vc16 (x64)	2m 44s
linux-debug	1m 28s
macos-debug	1m 20s
windows-debug	2m 49s
	3h 13m 46s

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