[DAGCombiner] Use getAPIntValue() instead of getZExtValue() where possible.
[DAGCombiner] Use getAPIntValue() instead of getZExtValue() where possible.

Better handling of out-of-i64-range values due to large integer types or from fuzz tests.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@363955 91177308-0d34-0410-b5e6-96231b3b80d8

GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm