Add permission bits to open with O_CREAT.

It's an error to pass open O_CREAT without giving it mode bits:
https://linux.die.net/man/3/open

Given that we never seem to do anything with the file but delete it,
0600 seems fine.

Bug: 32073964
Test: Now builds with clang FORTIFY.
Change-Id: Ia68463144b32475a470d39530a1fcaa0b52825ca
1 file changed