Keep the killed/dead sets sorted, so that "KillsRegister" can do a quick

binary search to test for membership.  This speeds up LLC a bit more on KC++,
e.g. on itanium from 16.6974s to 14.8272s, PPC from 11.4926s to 10.7089s and
X86 from 10.8128s to 9.7943s, with no difference in generated code (like all
of the RA patches).

With these changes, isel is the slowest pass for PPC/X86, but linscan+live
intervals is still > 50% of the compile time for itanium.  More work could
be done, but this is the last for now.

llvm-svn: 22993