Codegen: LICM Remove check for exactly 1 register def.

Codegen: LICM Remove check for exactly 1 register def.

When considering whether to split an instruction with a memory operand
into an explicit load and a register-based instruction, we currently
check that the resulting instruction has exactly 1 def. This prevents 2
important LICM optimizations: compares with memory operands, and double
indirect calls. All the tests and the test-suite pass without the check.
My guess as to original intent is to limit the additional register pressure
created by the new instruction, but given that we only split out a single
register, it is already limited.

The licm-dominance test now checks actual memory loads for hoisting instead of
undef, and it tests compares.
hoist-invariant-load.ll now checks for 2 hoists, the intended hoist, and a bonus
from calling a got-relative function in a loop.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@273616 91177308-0d34-0410-b5e6-96231b3b80d8