Next step in Mips16 prologue/epilogue cleanup.
Save S2(reg 18) only when we are calling floating point stubs that
have a return value of float or complex. Some more work to make this
better but this is the first step.




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@196921 91177308-0d34-0410-b5e6-96231b3b80d8