Add support for copying bool constants to registers.

Add support for copying bool constants to registers.
Disable the code that copies long constants to registers - it looks fishy.
Implement some simple casts: integral, smaller than longs, and equal-width
 or narrowing only.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@13413 91177308-0d34-0410-b5e6-96231b3b80d8