Use the "undergoes default argument promotion" bit on parameters to

Use the "undergoes default argument promotion" bit on parameters to
simplify the logic of initializing function parameters so that we don't need
both a variable declaration and a type in FunctionArgList.  This also means
that we need to propagate the CGFunctionInfo down in a lot of places rather
than recalculating it from the FAL.  There's more we can do to eliminate
redundancy here, and I've left FIXMEs behind to do it.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@127314 91177308-0d34-0410-b5e6-96231b3b80d8