[ExecutionEngine] Add a getSymbolTable method to RuntimeDyld.

This can be used to extract the symbol table from a RuntimeDyld instance prior
to disposing of it.

This patch also updates RTDyldObjectLinkingLayer to use the new method, rather
than requesting symbols one at a time via getSymbol.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@327476 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed