cmake: Set CMP0056 to NEW

When Android is compiled with "-static" in CMAKE_EXE_LINKER_FLAGS, only the
shared version of libc has utimensat.  By setting CMP0056 to NEW,
CMAKE_EXE_LINKER_FLAGS is passed to the try_compile in KWSYS_PLATFORM_CXX_TEST
so KWSYS_CXX_HAS_UTIMENSAT gets the correct result.

Change-Id: Ia5ff7abaafb92e043927b57c5f2858259195235f