Split each select function for a particular opcode into multiple ones. One

Split each select function for a particular opcode into multiple ones. One
per possible ValueType of the node. e.g. Select_add is split into Select_add_i8,
Select_add_i16, etc.

For opcodes which do not produce a non-chain result, it is split on the
ValueType of its first non-chain operand. e.g. Select_store.

On X86 / Mac OS X, Select_store used to be the largest function. It had a stack
frame size of 8.5k. Now the largest one is Store_i32 with a frame size of 3.1k.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@29404 91177308-0d34-0410-b5e6-96231b3b80d8