Make sure core components not depend on gtest (#6921)

Summary:
We recently removed the dependencies of core components on gtest. Add a Travis test to make sure it doesn't regress. Change cmake setting so that the gtest related components are only included when tests, benchmarks or stress tools are included in the build. Add this build setting in Travis to confirm it.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6921

Test Plan: See Travis passes

Reviewed By: ajkr

Differential Revision: D21863564

fbshipit-source-id: df26f50a8305a04ff19ffa8069a1857ecee10289

.travis.yml

@@ -310,7 +310,7 @@ script:
           ;;
       esac
 
-      mkdir build && cd build && cmake -DJNI=1 .. -DCMAKE_BUILD_TYPE=Release $OPT && make -j4 rocksdb rocksdbjni
+      mkdir build && cd build && cmake -DCMAKE_BUILD_TYPE=Release -DWITH_TESTS=0 -DWITH_GFLAGS=0 -DWITH_BENCHMARK_TOOLS=0 -DWITH_TOOLS=0 -DWITH_CORE_TOOLS=1 .. && make -j4 && cd  .. && rm -rf build && mkdir build && cd build && cmake -DJNI=1 .. -DCMAKE_BUILD_TYPE=Release $OPT && make -j4 rocksdb rocksdbjni
       ;;
     make-gcc4.8)
       OPT=-DTRAVIS V=1 SKIP_LINK=1 make -j4 all && [ "Linking broken because libgflags compiled with newer ABI" ]

CMakeLists.txt

@@ -523,7 +523,6 @@ endif()
 
 include_directories(${PROJECT_SOURCE_DIR})
 include_directories(${PROJECT_SOURCE_DIR}/include)
-include_directories(SYSTEM ${PROJECT_SOURCE_DIR}/third-party/gtest-1.8.1/fused-src)
 if(WITH_FOLLY_DISTRIBUTED_MUTEX)
   include_directories(${PROJECT_SOURCE_DIR}/third-party/folly)
 endif()
@@ -890,6 +889,16 @@ else()
 endif()
 
 option(WITH_JNI "build with JNI" OFF)
+# Tests are excluded from Release builds
+CMAKE_DEPENDENT_OPTION(WITH_TESTS "build with tests" ON
+  "CMAKE_BUILD_TYPE STREQUAL Debug" OFF)
+option(WITH_BENCHMARK_TOOLS "build with benchmarks" ON)
+option(WITH_CORE_TOOLS "build with ldb and sst_dump" ON)
+option(WITH_TOOLS "build with tools" ON)
+
+if(WITH_TESTS OR WITH_BENCHMARK_TOOLS OR WITH_TOOLS OR WITH_JNI OR JNI)
+  include_directories(SYSTEM ${PROJECT_SOURCE_DIR}/third-party/gtest-1.8.1/fused-src)
+endif()
 if(WITH_JNI OR JNI)
   message(STATUS "JNI library is enabled")
   add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/java)
@@ -965,15 +974,11 @@ if(NOT WIN32 OR ROCKSDB_INSTALL_ON_WINDOWS)
   )
 endif()
 
-# Tests are excluded from Release builds
-CMAKE_DEPENDENT_OPTION(WITH_TESTS "build with tests" ON
-  "CMAKE_BUILD_TYPE STREQUAL Debug" OFF)
 if(WITH_TESTS)
   add_subdirectory(third-party/gtest-1.8.1/fused-src/gtest)
   add_library(testharness STATIC
   test_util/testharness.cc)
   target_link_libraries(testharness gtest)
-
   set(TESTS
         cache/cache_test.cc
         cache/lru_cache_test.cc
@@ -1206,7 +1211,6 @@ if(WITH_TESTS)
   endif()
 endif()
 
-option(WITH_BENCHMARK_TOOLS "build with benchmarks" ON)
 if(WITH_BENCHMARK_TOOLS)
   add_executable(db_bench
     tools/db_bench.cc
@@ -1245,8 +1249,6 @@ if(WITH_BENCHMARK_TOOLS)
     ${ROCKSDB_LIB})
 endif()
 
-option(WITH_CORE_TOOLS "build with ldb and sst_dump" ON)
-option(WITH_TOOLS "build with tools" ON)
 if(WITH_CORE_TOOLS OR WITH_TOOLS)
   add_subdirectory(tools)
   add_custom_target(core_tools