Allow disabling build of vendored gtest with new cmake option EXTERNAL_GTEST

[duncanmmacleod]

This PR adds a new CMake option EXTERNAL_GTEST (default OFF) which allows disabling the build of the vendored gtest for the test suite.

I also added -DBUILD_UNITTESTS:BOOL=TRUE -DEXTERNAL_GTEST:BOOL=TRUE and a %check section to the rpm build to run the tests there. EDIT: this was dropped because EPEL7's gtest is too old, and adding a bunch of %if macros in the spec file seemed like a lot of work...

Fixed #46.

[djw8605]

I presume you tested all of this? Otherwise, it looks good.

[duncanmmacleod]

@djw8605, here's the log of a build that uses the EXTERNAL_GTEST option. Notice that gtest isn't built on-the-fly, but the tests run fine.

$ bash -ex build.sh
+ rm -rf _build
+ mkdir _build
+ cd _build
+ pwd
+ cmake .. -DCMAKE_INSTALL_PREFIX=/home/duncan/git/scitokens-cpp-fork/_build/_inst -DBUILD_UNITTESTS:BOOL=TRUE -DEXTERNAL_GTEST:BOOL=TRUE
-- The C compiler identification is GNU 9.3.0
-- The CXX compiler identification is GNU 9.3.0
-- Check for working C compiler: /home/duncan/opt/miniconda3/envs/py39/bin/x86_64-conda-linux-gnu-cc
-- Check for working C compiler: /home/duncan/opt/miniconda3/envs/py39/bin/x86_64-conda-linux-gnu-cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /home/duncan/opt/miniconda3/envs/py39/bin/x86_64-conda-linux-gnu-c++
-- Check for working CXX compiler: /home/duncan/opt/miniconda3/envs/py39/bin/x86_64-conda-linux-gnu-c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Found CURL: /home/duncan/opt/miniconda3/envs/py39/lib/libcurl.so (found version "7.76.1")
-- Looking for uuid_generate
-- Looking for uuid_generate - not found
-- Found UUID : /home/duncan/opt/miniconda3/envs/py39/lib/libuuid.so
-- Found PkgConfig: /home/duncan/opt/miniconda3/envs/py39/bin/pkg-config (found version "0.29.2")
-- Checking for module 'libcrypto'
--   Found libcrypto, version 1.1.1k
-- Checking for module 'openssl'
--   Found openssl, version 1.1.1k
-- Checking for module 'sqlite3'
--   Found sqlite3, version 3.35.5
-- Configuring done
CMake Warning (dev) at test/CMakeLists.txt:3 (add_dependencies):
  Policy CMP0046 is not set: Error on non-existent dependency in
  add_dependencies.  Run "cmake --help-policy CMP0046" for policy details.
  Use the cmake_policy command to set the policy and suppress this warning.

  The dependency target "gtest" of target "scitokens-gtest" does not exist.
This warning is for project developers.  Use -Wno-dev to suppress it.

-- Generating done
-- Build files have been written to: /home/duncan/git/scitokens-cpp-fork/_build
+ cmake --build .
Scanning dependencies of target SciTokens
[  6%] Building CXX object CMakeFiles/SciTokens.dir/src/scitokens.cpp.o
[ 12%] Building CXX object CMakeFiles/SciTokens.dir/src/scitokens_internal.cpp.o
[ 18%] Building CXX object CMakeFiles/SciTokens.dir/src/scitokens_cache.cpp.o
[ 25%] Linking CXX shared library libSciTokens.so
[ 25%] Built target SciTokens
Scanning dependencies of target scitokens-test
[ 31%] Building CXX object CMakeFiles/scitokens-test.dir/src/test.cpp.o
[ 37%] Linking CXX executable scitokens-test
[ 37%] Built target scitokens-test
Scanning dependencies of target scitokens-create
[ 43%] Building CXX object CMakeFiles/scitokens-create.dir/src/create.cpp.o
[ 50%] Linking CXX executable scitokens-create
[ 50%] Built target scitokens-create
Scanning dependencies of target scitokens-list-access
[ 56%] Building CXX object CMakeFiles/scitokens-list-access.dir/src/list_access.cpp.o
[ 62%] Linking CXX executable scitokens-list-access
[ 62%] Built target scitokens-list-access
Scanning dependencies of target scitokens-verify
[ 68%] Building CXX object CMakeFiles/scitokens-verify.dir/src/verify.cpp.o
[ 75%] Linking CXX executable scitokens-verify
[ 75%] Built target scitokens-verify
Scanning dependencies of target scitokens-test-access
[ 81%] Building CXX object CMakeFiles/scitokens-test-access.dir/src/test_access.cpp.o
[ 87%] Linking CXX executable scitokens-test-access
[ 87%] Built target scitokens-test-access
Scanning dependencies of target scitokens-gtest
[ 93%] Building CXX object test/CMakeFiles/scitokens-gtest.dir/main.cpp.o
[100%] Linking CXX executable scitokens-gtest
[100%] Built target scitokens-gtest
+ ctest -V
UpdateCTestConfiguration  from :/home/duncan/git/scitokens-cpp-fork/_build/DartConfiguration.tcl
UpdateCTestConfiguration  from :/home/duncan/git/scitokens-cpp-fork/_build/DartConfiguration.tcl
Test project /home/duncan/git/scitokens-cpp-fork/_build
Constructing a list of tests
Done constructing a list of tests
Updating test list for fixtures
Added 0 tests to meet fixture requirements
Checking test dependency graph...
Checking test dependency graph end
test 1
    Start 1: unit

1: Test command: /home/duncan/git/scitokens-cpp-fork/_build/test/scitokens-gtest
1: Test timeout computed to be: 10000000
1: [==========] Running 6 tests from 2 test suites.
1: [----------] Global test environment set-up.
1: [----------] 2 tests from SciTokenTest
1: [ RUN      ] SciTokenTest.CreateToken
1: [       OK ] SciTokenTest.CreateToken (0 ms)
1: [ RUN      ] SciTokenTest.SignToken
1: [       OK ] SciTokenTest.SignToken (1 ms)
1: [----------] 2 tests from SciTokenTest (1 ms total)
1:
1: [----------] 4 tests from SerializeTest
1: [ RUN      ] SerializeTest.VerifyTest
1: [       OK ] SerializeTest.VerifyTest (17 ms)
1: [ RUN      ] SerializeTest.TestStringList
1: [       OK ] SerializeTest.TestStringList (5 ms)
1: [ RUN      ] SerializeTest.VerifyWLCGTest
1: [       OK ] SerializeTest.VerifyWLCGTest (5 ms)
1: [ RUN      ] SerializeTest.FailVerifyToken
1: [       OK ] SerializeTest.FailVerifyToken (5 ms)
1: [----------] 4 tests from SerializeTest (32 ms total)
1:
1: [----------] Global test environment tear-down
1: [==========] 6 tests from 2 test suites ran. (33 ms total)
1: [  PASSED  ] 6 tests.
1/1 Test #1: unit .............................   Passed    0.04 sec

100% tests passed, 0 tests failed out of 1

Total Test time (real) =   0.04 sec
+ cmake --build . --target install
[ 25%] Built target SciTokens
[ 37%] Built target scitokens-test
[ 50%] Built target scitokens-create
[ 62%] Built target scitokens-list-access
[ 75%] Built target scitokens-verify
[ 87%] Built target scitokens-test-access
[100%] Built target scitokens-gtest
Install the project...
-- Install configuration: ""
-- Installing: /home/duncan/git/scitokens-cpp-fork/_build/_inst/lib/libSciTokens.so.0.0.2
-- Installing: /home/duncan/git/scitokens-cpp-fork/_build/_inst/lib/libSciTokens.so.0
-- Installing: /home/duncan/git/scitokens-cpp-fork/_build/_inst/lib/libSciTokens.so
-- Installing: /home/duncan/git/scitokens-cpp-fork/_build/_inst/include/scitokens/scitokens.h

[djw8605]

Neat! Sounds great!