FORTIFY_SOURCE: Add openat, fix bug

Add fortify_source support for openat(). This change requires that
an argument be supplied when using O_CREAT.

Fix unnecessary call to __open_2. If, at compile time, we know that
"flags" is constant and DOESN'T contain O_CREAT, the call to __open_2
is useless.

Change-Id: Ifcd29c4fb25e25656961d7552d672e161f0cfdbd
2 files changed