Change CMake googletest download location in docs

Change CMAKE_BINARY_DIR to CMAKE_CURRENT_BINARY_DIR
Able to use in a subfolder's CMakeLists.txt

googletest/README.md

@@ -124,8 +124,8 @@ include(ExternalProject)
 ExternalProject_Add(googletest
   GIT_REPOSITORY    https://github.com/google/googletest.git
   GIT_TAG           master
-  SOURCE_DIR        "${CMAKE_BINARY_DIR}/googletest-src"
-  BINARY_DIR        "${CMAKE_BINARY_DIR}/googletest-build"
+  SOURCE_DIR        "${CMAKE_CURRENT_BINARY_DIR}/googletest-src"
+  BINARY_DIR        "${CMAKE_CURRENT_BINARY_DIR}/googletest-build"
   CONFIGURE_COMMAND ""
   BUILD_COMMAND     ""
   INSTALL_COMMAND   ""
@@ -140,13 +140,13 @@ Existing build's `CMakeLists.txt`:
 configure_file(CMakeLists.txt.in googletest-download/CMakeLists.txt)
 execute_process(COMMAND ${CMAKE_COMMAND} -G "${CMAKE_GENERATOR}" .
   RESULT_VARIABLE result
-  WORKING_DIRECTORY ${CMAKE_BINARY_DIR}/googletest-download )
+  WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/googletest-download )
 if(result)
   message(FATAL_ERROR "CMake step for googletest failed: ${result}")
 endif()
 execute_process(COMMAND ${CMAKE_COMMAND} --build .
   RESULT_VARIABLE result
-  WORKING_DIRECTORY ${CMAKE_BINARY_DIR}/googletest-download )
+  WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/googletest-download )
 if(result)
   message(FATAL_ERROR "Build step for googletest failed: ${result}")
 endif()
@@ -157,8 +157,8 @@ set(gtest_force_shared_crt ON CACHE BOOL "" FORCE)
 
 # Add googletest directly to our build. This defines
 # the gtest and gtest_main targets.
-add_subdirectory(${CMAKE_BINARY_DIR}/googletest-src
-                 ${CMAKE_BINARY_DIR}/googletest-build
+add_subdirectory(${CMAKE_CURRENT_BINARY_DIR}/googletest-src
+                 ${CMAKE_CURRENT_BINARY_DIR}/googletest-build
                  EXCLUDE_FROM_ALL)
 
 # The gtest/gtest_main targets carry header search path