build: rely on gtest_main target instead of custom (#4396)

cmake/VowpalWabbitUtils.cmake

@@ -253,16 +253,6 @@ function(vw_add_executable)
   endif()
 endfunction()
 
-
-set(GTEST_MAIN_FILE_CONTENTS "#include <gtest/gtest.h>\n\
-\n\
-int main(int argc, char** argv)\n\
-{\n\
-  ::testing::InitGoogleTest(&argc, argv);\n\
-  return RUN_ALL_TESTS();\n\
-}\n"
-)
-
 function(vw_add_test_executable)
   cmake_parse_arguments(VW_TEST
   ""
@@ -286,13 +276,11 @@ function(vw_add_test_executable)
 
     vw_get_test_target(FULL_TEST_NAME ${VW_TEST_FOR_LIB})
 
-    file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/${FULL_TEST_NAME}_main.cc "${GTEST_MAIN_FILE_CONTENTS}")
-
-    add_executable(${FULL_TEST_NAME} ${CMAKE_CURRENT_BINARY_DIR}/${FULL_TEST_NAME}_main.cc ${VW_TEST_SOURCES})
+    add_executable(${FULL_TEST_NAME} ${VW_TEST_SOURCES})
     target_link_libraries(${FULL_TEST_NAME} PUBLIC
       ${FULL_FOR_LIB_NAME}
       ${VW_TEST_EXTRA_DEPS}
-      GTest::gmock GTest::gtest
+      GTest::gmock GTest::gtest_main
     )
     target_compile_definitions(${FULL_TEST_NAME} PRIVATE ${VW_TEST_COMPILE_DEFS})
     target_compile_options(${FULL_TEST_NAME} PRIVATE ${WARNING_OPTIONS} ${WARNING_AS_ERROR_OPTIONS})