Also attempt trivial coalescing for live intervals that end in a copy.

Also attempt trivial coalescing for live intervals that end in a copy.

The coalescer is supposed to clean these up, but when setting up parameters
for a function call, there may be copies to physregs. If the defining
instruction has been LICM'ed far away, the coalescer won't touch it.

The register allocation hint does not always work - when the register
allocator is backtracking, it clears the hints.

This patch takes care of a few more cases that r90163 missed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90502 91177308-0d34-0410-b5e6-96231b3b80d8