check for PR_SET_NAME being defined

Depending on what glibc/kernel headers you are compiling against,
PR_SET_NAME may or may not be defined.  Do the right thing if
PR_SET_NAME isn't defined and skip setting the process name.

Signed-off-by: Nathan Froyd <froydnj@codesourcery.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Message-Id: 
