[OCaml] Expose Llvm_executionengine.ExecutionEngine.create_mcjit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220619 91177308-0d34-0410-b5e6-96231b3b80d8
[OCaml] Unbreak Llvm_executionengine.initialize_native_target.

First, return true on success, as it is the OCaml convention.
Second, also initialize the native assembly printer, which is,
despite the name, required for MCJIT operation.

Since this function did not initialize the assembly printer earlier
and no function to initialize native assembly printer was available
elsewhere, it is safe to break its interface: it means that it
simply could not be used successfully before.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220620 91177308-0d34-0410-b5e6-96231b3b80d8
[OCaml] hexagon can't run MCJIT tests, XFAIL it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220621 91177308-0d34-0410-b5e6-96231b3b80d8
Fix LSR compile time.

This is a simple fix that brings the compilation time from 5min to 5s
on a specific real-world example. It's a large chain of computation in
a crypto routine (always a problem for SCEV). A unit test is not
feasible and there would be no way to check it. The fix is just basic
good practice for dealing with SCEVs, there's no risk of regression.

Patch by Daniel Reynaud!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220622 91177308-0d34-0410-b5e6-96231b3b80d8