[llvm-exegesis] Pass data layout explicitly to LLJIT (#190789)
This is a defesive change that aims to make sure the target data layout
of both the object compilation and LLJIT is the same, by passing it
explicitly rather than relying similar auto-detection implicitly.
The patch doesnt add a new test but relies on existing ones, as a test
case of different layouts would require to exhibit a misuse of the tool,
doing cross-compilation to change the layout of the compilation. The
tool is not designed to work this way.