build: add `--shared-gtest` configure flag #2123

Job	Run time
Build slim tarball	1m 30s
aarch64-darwin: with shared libraries	27m 16s
aarch64-linux: with shared libraries	23m 21s
x86_64-linux: with shared libraries	27m 52s
x86_64-darwin: with shared libraries	40m 14s
	2h 0m 13s

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