* Reuse gtest on the system
Try to use gtest on the system if found. Avoid using recent CMake
features.
* Set CMP0135 only when using FetchContent
* Add /bigobj option for MSVC
* Support also cmake between 3.14 and 3.20
Older versions provided only GTest::Main target, not currently used
gtest_main. Provide backward compatibility also to old cmake versions.
* Remove redundant variable checking
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Co-authored-by: Jiwoo Park <jiwoo_90@naver.com>
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