AA metadata refactoring (introduce AAMDNodes)

In order to enable the preservation of noalias function parameter information
after inlining, and the representation of block-level __restrict__ pointer
information (etc.), additional kinds of aliasing metadata will be introduced.
This metadata needs to be carried around in AliasAnalysis::Location objects
(and MMOs at the SDAG level), and so we need to generalize the current scheme
(which is hard-coded to just one TBAA MDNode*).

This commit introduces only the necessary refactoring to allow for the
introduction of other aliasing metadata types, but does not actually introduce
any (that will come in a follow-up commit). What it does introduce is a new
AAMDNodes structure to hold all of the aliasing metadata nodes associated with
a particular memory-accessing instruction, and uses that structure instead of
the raw MDNode* in AliasAnalysis::Location, etc.

No functionality change intended.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213859 91177308-0d34-0410-b5e6-96231b3b80d8

unittests/Analysis/MixedTBAATest.cpp

@@ -65,7 +65,7 @@ TEST_F(MixedTBAATest, MixedTBAA) {
   // Run the TBAA eval pass on a mixture of path-aware and non-path-aware TBAA.
   // The order of the metadata (path-aware vs non-path-aware) is important,
   // because the AA eval pass only runs one test per store-pair.
-  const char* args[] = { "MixedTBAATest", "-evaluate-tbaa" };
+  const char* args[] = { "MixedTBAATest", "-evaluate-aa-metadata" };
   cl::ParseCommandLineOptions(sizeof(args) / sizeof(const char*), args);
   PM.add(createTypeBasedAliasAnalysisPass());
   PM.add(createAAEvalPass());