Issue Description:

Stack overflow 2: revenge of the rdar://55929175

After implementing formatting in sourcekit-lsp I was investigating why it wasn't working for things that are nested four levels deep. After fighting with debugger, I had a hunch that it may be stack overflow. I found a comment in the function that was crashing:

    // The implementation of every generated case goes into its own function. This
    // circumvents an issue where the compiler allocates stack space for every
    // case statement next to each other in debug builds, causing it to allocate
    // ~50KB per call to this function. rdar://55929175

It crashes only in debug mode, on macos

To reproduce:

• clone https://github.com/Trzyipolkostkicukru/sourcekit-lsp/tree/format and checkout commit ed642036f4b9ce7696ad340523ed8e9b4bdb9761

• get toolchain swift-DEVELOPMENT-SNAPSHOT-2020-01-29-a and set it as your compiler

• compile and set up sourcekit-lsp

• try to format a file with 4+ levels of nesting, for example:

  do {
  do { do { do { print("Hello, world") } } } 
  }