Fully Reformat fallback_malloc.cpp

This patch fully reformats fallback_malloc.cpp. Previously the test
was a mess of different styles and indentations. This made it very
hard to work in and read. Therefore I felt it was best to re-format
the whole thing.

Unfortuantly this means some history will be lost, but hopefully
much of it will still be accessible after ignoring whitespace changes.

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@296960 91177308-0d34-0410-b5e6-96231b3b80d8