[docs] Add a pointer to ExitOnError to the discussion of handleErrors in the programmer's manual.
[docs] Add a pointer to ExitOnError to the discussion of handleErrors in the
programmer's manual.

ExitOnError is often a better alternative to handleErrors for tool code. This
patch makes it easier to find the ExitOnError discussion when reading the
handleErrors section.

Thanks to Peter Collingbourne for the suggestion.



git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@286167 91177308-0d34-0410-b5e6-96231b3b80d8

GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm