Import helper cmake script to find GMock and GTest on more modern systems

Taken from https://code.launchpad.net/~cmake-extras/cmake-extras/trunk

cmake/FindGMock.cmake

+# Copyright (C) 2014 Canonical Ltd
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License version 3 as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Build with system gmock and embedded gtest
+#
+# Usage:
+#
+# find_package(GMock)
+#
+# ...
+#
+# target_link_libraries(
+#   my-target
+#   ${GTEST_BOTH_LIBRARIES}
+# )
+#
+# NOTE: Due to the way this package finder is implemented, do not attempt
+# to find the GMock package more than once.
+
+find_package(Threads)
+
+if (EXISTS "/usr/src/googletest")
+    # As of version 1.8.0
+    set(GMOCK_SOURCE_DIR "/usr/src/googletest/googlemock" CACHE PATH "gmock source directory")
+    set(GMOCK_INCLUDE_DIRS "${GMOCK_SOURCE_DIR}/include" CACHE PATH "gmock source include directory")
+    set(GTEST_INCLUDE_DIRS "/usr/src/googletest/googletest/include" CACHE PATH "gtest source include directory")
+else()
+    set(GMOCK_SOURCE_DIR "/usr/src/gmock" CACHE PATH "gmock source directory")
+    set(GMOCK_INCLUDE_DIRS "/usr/include" CACHE PATH "gmock source include directory")
+    set(GTEST_INCLUDE_DIRS "/usr/include" CACHE PATH "gtest source include directory")
+endif()
+
+# We add -g so we get debug info for the gtest stack frames with gdb.
+# The warnings are suppressed so we get a noise-free build for gtest and gmock if the caller
+# has these warnings enabled.
+set(findgmock_cxx_flags "${CMAKE_CXX_FLAGS} -g -Wno-old-style-cast -Wno-missing-field-initializers -Wno-ctor-dtor-privacy -Wno-switch-default")
+
+set(findgmock_bin_dir "${CMAKE_CURRENT_BINARY_DIR}/gmock")
+set(findgmock_gtest_lib "${findgmock_bin_dir}/gtest/libgtest.a")
+set(findgmock_gtest_main_lib "${findgmock_bin_dir}/gtest/libgtest_main.a")
+set(findgmock_gmock_lib "${findgmock_bin_dir}/libgmock.a")
+set(findgmock_gmock_main_lib "${findgmock_bin_dir}/libgmock_main.a")
+
+include(ExternalProject)
+ExternalProject_Add(GMock SOURCE_DIR "${GMOCK_SOURCE_DIR}"
+                          BINARY_DIR "${findgmock_bin_dir}"
+                          BUILD_BYPRODUCTS "${findgmock_gtest_lib}"
+                                           "${findgmock_gtest_main_lib}"
+                                           "${findgmock_gmock_lib}"
+                                           "${findgmock_gmock_main_lib}"
+                          INSTALL_COMMAND ""
+                          CMAKE_ARGS "-DCMAKE_CXX_FLAGS=${findgmock_cxx_flags}")
+
+add_library(gtest INTERFACE)
+target_include_directories(gtest INTERFACE ${GTEST_INCLUDE_DIRS})
+target_link_libraries(gtest INTERFACE ${findgmock_gtest_lib} ${CMAKE_THREAD_LIBS_INIT})
+add_dependencies(gtest GMock)
+
+add_library(gtest_main INTERFACE)
+target_include_directories(gtest_main INTERFACE ${GTEST_INCLUDE_DIRS})
+target_link_libraries(gtest_main INTERFACE ${findgmock_gtest_main_lib} gtest)
+
+add_library(gmock INTERFACE)
+target_include_directories(gmock INTERFACE ${GMOCK_INCLUDE_DIRS})
+target_link_libraries(gmock INTERFACE ${findgmock_gmock_lib} gtest)
+
+add_library(gmock_main INTERFACE)
+target_include_directories(gmock_main INTERFACE ${GMOCK_INCLUDE_DIRS})
+target_link_libraries(gmock_main INTERFACE ${findgmock_gmock_main_lib} gmock)
+
+set(GTEST_LIBRARIES gtest)
+set(GTEST_MAIN_LIBRARIES gtest_main)
+set(GMOCK_LIBRARIES gmock gmock_main)
+set(GTEST_BOTH_LIBRARIES ${GTEST_LIBRARIES} ${GTEST_MAIN_LIBRARIES})
+
+unset(findgmock_cxx_flags)
+unset(findgmock_bin_dir)
+unset(findgmock_gtest_lib)
+unset(findgmock_gtest_main_lib)
+unset(findgmock_gmock_lib)
+unset(findgmock_gmock_main_lib)