Use shared gtest instead of submodule

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 617e4b2..2857875 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -18,7 +18,6 @@ set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${CMAKE_SOURCE_DIR}/cmake/Modules/")
 include(GNUInstallDirs)
 
 project(leelaz)
-add_subdirectory(gtest EXCLUDE_FROM_ALL) # We don't want to install gtest, exclude it from `all`
 
 # Required Packages
 set(Boost_MIN_VERSION "1.58.0")
@@ -27,6 +26,7 @@ find_package(Boost 1.58.0 REQUIRED program_options filesystem)
 find_package(Threads REQUIRED)
 find_package(ZLIB REQUIRED)
 find_package(OpenCL REQUIRED)
+find_package(GTest REQUIRED)
 # We need OpenBLAS for now, because we make some specific
 # calls. Ideally we'd use OpenBLAS is possible and fall back to
 # not doing those calls if it's not present.
@@ -93,6 +93,7 @@ include_directories(${IncludePath})
 include_directories(${Boost_INCLUDE_DIRS})
 include_directories(${OpenCL_INCLUDE_DIRS})
 include_directories(${ZLIB_INCLUDE_DIRS})
+include_directories(${GTEST_INCLUDE_DIRS})
 
 if((UNIX AND NOT APPLE) OR WIN32)
     include_directories(${BLAS_INCLUDE_DIRS})
@@ -141,7 +142,8 @@ target_link_libraries(tests ${Boost_LIBRARIES})
 target_link_libraries(tests ${BLAS_LIBRARIES})
 target_link_libraries(tests ${OpenCL_LIBRARIES})
 target_link_libraries(tests ${ZLIB_LIBRARIES})
-target_link_libraries(tests gtest_main ${CMAKE_THREAD_LIBS_INIT})
+target_link_libraries(tests ${GTEST_BOTH_LIBRARIES})
+target_link_libraries(tests ${CMAKE_THREAD_LIBS_INIT})
 
 include(GetGitRevisionDescription)
 git_describe(VERSION --tags)
d-aux/test-env.in'>
<input type='hidden' name='id' value='7996bd3955bc3ce799bf41a3195f6188b44b7234'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=7996bd3955bc3ce799bf41a3195f6188b44b7234'>root</a>/<a href='/guix/log/build-aux?id=7996bd3955bc3ce799bf41a3195f6188b44b7234'>build-aux</a>/<a href='/guix/log/build-aux/test-env.in?id=7996bd3955bc3ce799bf41a3195f6188b44b7234'>test-env.in</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/build-aux/test-env.in?id=7996bd3955bc3ce799bf41a3195f6188b44b7234&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-12-22 10:53:19 +0100'>2021-12-22</span></td><td><a href='/guix/commit/build-aux/test-env.in?id=9ebc9ca070a21ba0aeb3f61202a8071bb250ccc8'>tests: Move keys into ./tests/keys/ and add a third ed25519 key.</a><span class='msg-avail'>...<span class='msg-tooltip'>The third key will be used in an upcoming commit.

Rename public keys to .pub.

* guix/tests/gnupg.scm (%ed25519-3-public-key-file): New variable.
(%ed25519-3-secret-key-file): New variable.
(%ed25519-2-public-key-file): Renamed from %ed25519bis-public-key-file.
(%ed25519-2-secret-key-file): Renamed from %ed25519bis-secret-key-file.
* tests/keys/ed25519-3.key: New file.
* tests/keys/ed25519-3.sec: New file.

Signed-off-by: Mathieu Othacehe &lt;othacehe@gnu.org&gt;
</span></span></td><td>Attila Lendvai</td></tr>
<tr><td><span title='2021-04-20 12:13:16 +0200'>2021-04-20</span></td><td><a href='/guix/commit/build-aux/test-env.in?id=d95168321f4a9bf6857b598da0a183b45a868d54'>import: Remove Nix importer.</a><span class='msg-avail'>...<span class='msg-tooltip'>This importer has suffered from bitrot and no longer works with current
Nix and Nixpkgs.  See &lt;https://bugs.gnu.org/32339&gt; and
&lt;https://bugs.gnu.org/36255&gt;.

* guix/import/snix.scm, guix/scripts/import/nix.scm,
tests/snix.scm: Remove.
* Makefile.am (MODULES, SCM_TESTS): Remove them.
* guix/scripts/import.scm (importers): Remove "nix".
* build-aux/test-env.in: Remove NIXPKGS variable.
* configure.ac: Remove '--with-nixpkgs' option.
* doc/guix.texi (Invoking guix import): Remove bit about "guix import
nix".
* etc/completion/fish/guix.fish: Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>