Try to fix an SDAG dependence issue with sret

r208453 added support for having sret on the second parameter.  In that
change, the code for copying sret into a virtual register was hoisted
into the loop that lowers formal parameters.  This caused a "Wrong
topological sorting" assertion failure during scheduling when a
parameter is passed in memory.  This change undoes that by creating a
second loop that deals with sret.

I'm worried that this fix is incomplete.  I don't fully understand the
dependence issues.  However, with this change we produce the same DAGs
we used to produce, so if they are broken, they are just as broken as
they have always been.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208637 91177308-0d34-0410-b5e6-96231b3b80d8
Fix ARM bswap16.ll test on Windows

Windows on ARM only supports thumb mode execution, so we have to
explicitly pick some non-Windows OS to test ARM mode codegen.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208638 91177308-0d34-0410-b5e6-96231b3b80d8