[RuntimeDyld] Remove relocation bounds check introduced in r208375 (MachO only).

We do all of our address arithmetic in 64-bit, and operations involving
logically negative 32-bit offsets (actually represented as unsigned 64 bit ints)
often overflow into higher bits. The overflow check could be preserved by
casting to uint32 at the callsite for applyRelocationValue, but this would
eliminate the value of the check.

The right way to handle overflow in relocations is to make relocation processing
target specific, and compute the values for RelocationEntry objects in the
appropriate types (32-bit for 32-bit targets, 64-bit for 64-bit targets). This
is coming as part of the cleanup I'm working on.

This fixes another i386 regression test.

<rdar://problem/16889891>



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209536 91177308-0d34-0410-b5e6-96231b3b80d8
Add the extracted constant offset using GEP

Fixed a TODO in r207783.

Add the extracted constant offset using GEP instead of ugly
ptrtoint+add+inttoptr. Using GEP simplifies future optimizations and makes IR
easier to understand. 

Updated all affected tests, and added a new test in split-gep.ll to cover a
corner case where emitting uglygep is necessary.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209537 91177308-0d34-0410-b5e6-96231b3b80d8