syscall: don't assume we have a GETEUID system call

On Alpha GNU/Linux there is no geteuid system call, there is only
getresuid.  The raw geteuid system call is only used for testing, so
just skip the test if it's not available.

Change-Id: I2cc972da32d56767f61c8c6f4fa1872f74545c82
Reviewed-on: https://go-review.googlesource.com/137655
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
2 files changed