[asan] added flag -d|--demangle to asan_symbolize.py, makes addr2line/llvm-symbolizer demangle the functions names

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@175429 91177308-0d34-0410-b5e6-96231b3b80d8
[asan] enable asan_prelink_test when gold is the default linker (gold and bfd linker have different flag syntax)

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@175431 91177308-0d34-0410-b5e6-96231b3b80d8