Simplify and unify gtest build (learning-process#630)

- Disable gmock
 - Pass existing cmake variables if available
- Use `-Dgtest_force_shared_crt` only for gtest instead of the whole
project

Author: aobolensk

cmake/configure.cmake

@@ -1,7 +1,3 @@
-if(MSVC)
-  option(gtest_force_shared_crt "" TRUE)
-endif(MSVC)
-
 if(NOT CMAKE_BUILD_TYPE)
   set(CMAKE_BUILD_TYPE "Release")
 endif(NOT CMAKE_BUILD_TYPE)

cmake/gtest.cmake

@@ -11,10 +11,11 @@ ExternalProject_Add(
              -DCMAKE_C_COMPILER_LAUNCHER=${CMAKE_C_COMPILER_LAUNCHER}
              -DCMAKE_CXX_COMPILER_LAUNCHER=${CMAKE_CXX_COMPILER_LAUNCHER}
              -DCMAKE_CXX_STANDARD=${CMAKE_CXX_STANDARD}
-             -DCMAKE_CXX_STANDARD_REQUIRED=ON
+             -DCMAKE_CXX_STANDARD_REQUIRED=${CMAKE_CXX_STANDARD_REQUIRED}
              -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
              -DCMAKE_C_FLAGS=-w
              -DCMAKE_CXX_FLAGS=-w
+             -DBUILD_GMOCK=OFF
              $<$<BOOL:MSVC>:-Dgtest_force_shared_crt=ON>
   BUILD_COMMAND
     "${CMAKE_COMMAND}" --build