CMake: clean up setting of platform specific linker flags

Set flags directly on the target, and use common function for all cases.
This refactoring helps with the next commit for test executables.

Ref D8714

tests/gtests/runner/CMakeLists.txt

@@ -51,7 +51,7 @@ BLENDER_SRC_GTEST_EX(
   EXTRA_LIBS "${TEST_LIBS}"
   SKIP_ADD_TEST
 )
-setup_liblinks(blender_test)
+setup_platform_linker_libs(blender_test)
 
 if(WIN32)
   foreach(_lib ${_test_libs})