build: add `--shared-gtest` configure flag #2065

Job	Run time
Build slim tarball	1m 30s
aarch64-linux: with shared libraries	1h 51m 40s
aarch64-darwin: with shared libraries	1h 0m 50s
x86_64-linux: with shared libraries	1h 35m 40s
x86_64-darwin: with shared libraries	2h 12m 40s
	6h 42m 20s

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