SectionMemoryManager shouldn't be a JITMemoryManager. Previously, the 
EngineBuilder interface required a JITMemoryManager even if it was being used 
to construct an MCJIT. But the MCJIT actually wants a RTDyldMemoryManager. 
Consequently, the SectionMemoryManager, which is meant for MCJIT, derived 
from the JITMemoryManager and then stubbed out a bunch of JITMemoryManager 
methods that weren't relevant to the MCJIT.

This patch fixes the situation: it teaches the EngineBuilder that 
RTDyldMemoryManager is a supertype of JITMemoryManager, and that it's 
appropriate to pass a RTDyldMemoryManager instead of a JITMemoryManager if 
we're using the MCJIT. This allows us to remove the stub methods from 
SectionMemoryManager, and make SectionMemoryManager a direct subtype of 
RTDyldMemoryManager.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181820 91177308-0d34-0410-b5e6-96231b3b80d8