Make tests compatible with older GTest and GCC (#17)

In particular, this allows the tests to build on RHEL 8.

Author: cottsay

test/CMakeLists.txt

@@ -10,6 +10,7 @@ find_package(GTest REQUIRED)
 macro(add_cache_test NAME)
   add_executable(test_${NAME} "main.cpp" "test_${NAME}.cpp")
   target_link_libraries(test_${NAME}
+    "$<$<AND:$<CXX_COMPILER_ID:GNU>,$<VERSION_LESS:$<CXX_COMPILER_VERSION>,9.0>>:-lstdc++fs>"
     ${GTEST_LIBRARIES}
     createrepo-cache)
   add_test(NAME ${NAME} COMMAND test_${NAME})
@@ -18,6 +19,7 @@ endmacro()
 macro(add_integration_test NAME)
   add_executable(test_${NAME} "integration_main.cpp" "test_${NAME}.cpp")
   target_link_libraries(test_${NAME}
+    "$<$<AND:$<CXX_COMPILER_ID:GNU>,$<VERSION_LESS:$<CXX_COMPILER_VERSION>,9.0>>:-lstdc++fs>"
     ${GTEST_LIBRARIES}
     createrepo-agent-lib)
   add_test(NAME ${NAME} COMMAND test_${NAME})

test/test_smoke.cpp

@@ -22,4 +22,4 @@ TEST_P(smoke, commit) {
   gpg_error_t rc = assuan_transact(client, "COMMIT", NULL, NULL, NULL, NULL, NULL, NULL);
   EXPECT_FALSE(rc);
 }
-INSTANTIATE_TEST_SUITE_P( , smoke, testing::Values("empty", "populated"), smoke::PrintParamName);
+INSTANTIATE_TEST_CASE_P(smoke, smoke, testing::Values("empty", "populated"), smoke::PrintParamName);