Transform: add SymbolRewriter pass

This introduces the symbol rewriter. This is an IR->IR transformation that is
implemented as a CodeGenPrepare pass. This allows for the transparent
adjustment of the symbols during compilation.

It provides a clean, simple, elegant solution for symbol inter-positioning. This
technique is often used, such as in the various sanitizers and performance
analysis.

The control of this is via a custom YAML syntax map file that indicates source
to destination mapping, so as to avoid having the compiler to know the exact
details of the source to destination transformations.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221548 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/Passes.cpp

@@ -27,6 +27,7 @@
 #include "llvm/Target/TargetLowering.h"
 #include "llvm/Target/TargetSubtargetInfo.h"
 #include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/SymbolRewriter.h"
 
 using namespace llvm;
 
@@ -445,6 +446,7 @@ void TargetPassConfig::addPassesToHandleExceptions() {
 void TargetPassConfig::addCodeGenPrepare() {
   if (getOptLevel() != CodeGenOpt::None && !DisableCGP)
     addPass(createCodeGenPreparePass(TM));
+  addPass(llvm::createRewriteSymbolsPass());
 }
 
 /// Add common passes that perform LLVM IR to IR transforms in preparation for