[Orc] Fix member variable ordering issue in OrcMCJITReplacement.

https://reviews.llvm.org/D36888

From that review description:

When an OrcMCJITReplacement object gets destructed, LazyEmitLayer may still
contain a shared_ptr of a module, which requires ShouldDelete in the deleter.
But ShouldDelete gets destructed before LazyEmitLayer due to the order of
declaration in OrcMCJITReplacement, which leads to a crash, when the destructor
of LazyEmitLayer is executed.  Changing the order of declaration fixes this.

Patch by Moritz Kroll. Thanks Moritz!

llvm-svn: 312086