FindGTest: Revert "Allow either "Debug" or "Release" configurations."

Revert commit a064b18f85 (FindGTest: Allow either "Debug" or "Release"
configurations., 2020-06-29, v3.19.0-rc1~584^2).  If both configurations
are found then `GTEST_LIBRARY` is populated in a way that breaks
`__gtest_determine_library_type`, and the imported target is not
created correctly.

Fixes: #21473
Issue: #17799

Modules/FindGTest.cmake

@@ -96,27 +96,6 @@ function(__gtest_find_library _name)
     mark_as_advanced(${_name})
 endfunction()
 
-function(__gtest_find_library_configuration _name _lib _cfg_suffix)
-    set(_libs ${_lib})
-    if(MSVC AND GTEST_MSVC_SEARCH STREQUAL "MD")
-        # The provided /MD project files for Google Test add -md suffixes to the
-        # library names.
-        list(INSERT _libs 0 ${_lib}-md)
-    endif()
-    list(TRANSFORM _libs APPEND "${_cfg_suffix}")
-
-    __gtest_find_library(${_name} ${_libs})
-endfunction()
-
-include(${CMAKE_CURRENT_LIST_DIR}/SelectLibraryConfigurations.cmake)
-function(__gtest_find_and_select_library_configurations _basename _lib)
-    __gtest_find_library_configuration(${_basename}_LIBRARY_RELEASE ${_lib} "")
-    __gtest_find_library_configuration(${_basename}_LIBRARY_DEBUG   ${_lib} "d")
-
-    select_library_configurations(${_basename})
-    set(${_basename}_LIBRARY ${${_basename}_LIBRARY} PARENT_SCOPE)
-endfunction()
-
 macro(__gtest_determine_windows_library_type _var)
     if(EXISTS "${${_var}}")
         file(TO_NATIVE_PATH "${${_var}}" _lib_path)
@@ -208,13 +187,18 @@ find_path(GTEST_INCLUDE_DIR gtest/gtest.h
 )
 mark_as_advanced(GTEST_INCLUDE_DIR)
 
-# Allow GTEST_LIBRARY and GTEST_MAIN_LIBRARY to be set manually, as the
-# locations of the gtest and gtest_main libraries, respectively.
-if(NOT GTEST_LIBRARY)
-    __gtest_find_and_select_library_configurations(GTEST gtest)
-endif()
-if(NOT GTEST_MAIN_LIBRARY)
-    __gtest_find_and_select_library_configurations(GTEST_MAIN gtest_main)
+if(MSVC AND GTEST_MSVC_SEARCH STREQUAL "MD")
+    # The provided /MD project files for Google Test add -md suffixes to the
+    # library names.
+    __gtest_find_library(GTEST_LIBRARY            gtest-md  gtest)
+    __gtest_find_library(GTEST_LIBRARY_DEBUG      gtest-mdd gtestd)
+    __gtest_find_library(GTEST_MAIN_LIBRARY       gtest_main-md  gtest_main)
+    __gtest_find_library(GTEST_MAIN_LIBRARY_DEBUG gtest_main-mdd gtest_maind)
+else()
+    __gtest_find_library(GTEST_LIBRARY            gtest)
+    __gtest_find_library(GTEST_LIBRARY_DEBUG      gtestd)
+    __gtest_find_library(GTEST_MAIN_LIBRARY       gtest_main)
+    __gtest_find_library(GTEST_MAIN_LIBRARY_DEBUG gtest_maind)
 endif()
 
 include(${CMAKE_CURRENT_LIST_DIR}/FindPackageHandleStandardArgs.cmake)