* Use alloca() to force GCC not to eliminate frame pointer

* Use alloca() to force GCC not to eliminate frame pointer
* Break apart saving and restoring registers into separate functions
* Instead of saving single and double FP registers, just save the double
  registers -- aliasing helps preserve the single FP registers as well.
* Request just as much memory for a stub as we actually use

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@8200 91177308-0d34-0410-b5e6-96231b3b80d8