Don't mangle \n and "

There is nothing special about quotes and newlines from the object
file point of view, only the assembler has to worry about expanding
the \n and \".

This patch then removes the special handling from the Mangler.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194667 91177308-0d34-0410-b5e6-96231b3b80d8