Fixed two issues in the type encoding parser:

- A correctness issue: with assertions disabled,
  ReadQuotedString would misbehave; and

- A performance issue: BuildType used a long
  chain of if()s; I changed that to two switch
  statements.  That also makes the code much
  nicer to step through when debugging it.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@221651 91177308-0d34-0410-b5e6-96231b3b80d8