Fix android-cloexec-pipe clang-tidy warning

The upcoming clang-tidy update finds a new instance of
android-cloexec-pipe warning:

FileUtilsTests.cpp:72:13: error: prefer pipe2() with O_CLOEXEC to avoid leaking file descriptors to child processes
ASSERT_EQ(pipe(pipefd), 0);
^~~~~~~~~~~~
pipe2(pipefd, O_CLOEXEC)

Apply the suggested fix by clang-tidy.

Test: build
Bug: 131328001
Change-Id: Iee772b5c3ed5e2af481e479dab19030f8419290a