Revert "Revert "adb: add support for O_CLOEXEC to unique_fd pipe wrapper.""

Implement pipe2 ourselves on darwin.

This reverts commit f139ba47a13de0637732af9fd70aab0e8c877e45.

Test: none!
Change-Id: I42c2a8d07712fe4ac75b5824f754e79a5b9f5cb4
1 file changed