Enable LLVM TBAA metadata
Enable LLVM TBAA metadata

[trivial and not reviewed]

Type-Based Alias Analysis metadata emission was disabled
in the LLVM backend because it needed more testing. I've
done the necessary testing:
 - test/users/ferguson has specific alias-analysis test cases
 - I've manually checked the LLVM IR for those tests
 - the Chapel test suite passes everything that should pass
    with --fast --llvm

So this patch enables LLVM TBAA metadata on loads and stores
in the code generator.



git-svn-id: 88467cb1fb04b8a755be7e1ee1026be4190196ef@21862 3a8e244f-b0f2-452b-bcba-4c88e055c3ca

sungeunchoi/chapel,hildeth/chapel,CoryMcCartan/chapel,CoryMcCartan/chapel,hildeth/chapel,hildeth/chapel,hildeth/chapel,CoryMcCartan/chapel,sungeunchoi/chapel,sungeunchoi/chapel,sungeunchoi/chapel,chizarlicious/chapel,CoryMcCartan/chapel,chizarlicious/chapel,hildeth/chapel,chizarlicious/chapel,sungeunchoi/chapel,chizarlicious/chapel,hildeth/chapel,sungeunchoi/chapel,chizarlicious/chapel,chizarlicious/chapel,sungeunchoi/chapel,sungeunchoi/chapel,CoryMcCartan/chapel,chizarlicious/chapel,CoryMcCartan/chapel,CoryMcCartan/chapel,hildeth/chapel