Provide workaround for PR 15130.

This changes the RecordingMemoryManager in lli to use mapped memory rather than malloc to allocate memory for sections and uses a 'near' MemoryBlock to keep the allocations together.  This works around a problem in MCJIT where relocations are applied to a generated image immediately oupon generation, which isn't appropriate for the remote case.

llvm-svn: 176057