[LightDM] Problem with LightDM on Solaris build

[Brian Cameron]

LightDM does not build on Solaris because Solaris does not have the
setresuid or setresgid functions.  These are used in the file
/src/privileges.c.  If I #ifdef out these calls, the LightDM code
otherwise builds okay.

Is the use of these functions necessary?  Would it make sense to #ifdef
the code so it can also build and work on Solaris?  Any advice about how
to make this code more portable would be appreciated.

Brian