statically link GTest, update to 1.18.0, fetch it with CPM

[jameslamb]

Closes #704

Proposes:

• statically linking GoogleTest
• getting GoogleTest via CPM for simplicity and cache-friendliness (mostly borrowing the approach I added to XGBoost in [c++] stop using dmlc-core's GTest, running its C++ tests xgboost#12494)

Notes for Reviewers

How I tested this

Using the reproducible example from #704.

# build tests
$ rm -rf ./build
$ cmake -B build -S . -DBUILD_SHARED_LIBS=ON -DBUILD_CPP_TEST=ON
$ cmake --build build -j8

# relocate the test executable
$ TMP_DIR=$(mktemp -d)
$ mv ./build/treelite_cpp_test "${TMP_DIR}/"
$ rm -rf ./build
$ pushd "${TMP_DIR}"

# try testing
$ ./treelite_cpp_test
...
[==========] 29 tests from 9 test suites ran. (11 ms total)
[  PASSED  ] 29 tests.

$ ldd ./treelite_cpp_test
        linux-vdso.so.1 (0x0000766f56a2e000)
        libgomp.so.1 => /lib/x86_64-linux-gnu/libgomp.so.1 (0x0000766f569bd000)
        libstdc++.so.6 => /lib/x86_64-linux-gnu/libstdc++.so.6 (0x0000766f56200000)
        libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x0000766f568d4000)
        libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x0000766f568a6000)
        libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x0000766f55e00000)
        /lib64/ld-linux-x86-64.so.2 (0x0000766f56a30000)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.97%. Comparing base (b0525f6) to head (f91ecf0).

Additional details and impacted files

@@            Coverage Diff            @@
##           mainline     #705   +/-   ##
=========================================
  Coverage     83.97%   83.97%           
=========================================
  Files            75       75           
  Lines          6908     6908           
  Branches        559      559           
=========================================
  Hits           5801     5801           
  Misses         1107     1107           

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[chyunsu3]

I'd love to use the latest GTest. Is there a disadvantage for upgrading?

[jameslamb]

Oh sure! I'm not aware of any disadvantage. Looks like it still has a CMake minimum of 3.16 (build link), and CI could tell us if it has any compiler support limitations or other problems like that (but I really doubt it for that project).

Also... statically linking it makes it even safer to upgrade this project to a different version 😁

I'll try that here.

[jameslamb]

I just tried locally on my Mac and tests seem to work fine with the latest version (1.18.0, released 3 weeks ago).

Pushed f91ecf0 with that upgrade + removing the MSVC stuff.

[chyunsu3]

Thanks!