- Added a hook processFunctionBeforeCalleeSaveScn(). This is called by PEI just

before it determines which callee-save registers are to be spilled. This allows
the target to make changes such as forcing certain physical registers to be
spilled.
- Modified comments. It's important to note the order of registers in the array
returns by getCalleeSaveRegs() determines the order of callee save spill code.

llvm-svn: 30635