Clean up su.

Stop building su as a static executable. We don't rely on the getuid
implementation for security, so we have nothing to fear from the dynamic
linker.

Add some missing error checking and improve error reporting.

Remove various special cases that can all be rolled into the general
case.

Bug: 19647373
Change-Id: I2689b8957a89da1f3be571fcdc966b1084efca9a
2 files changed