[SystemZ] Fix handling of pass-by-pointer arguments

I'd misunderstood getIndirect() to mean that the argument should be passed
as a pointer at the ABI level, with the ByVal argument choosing caller-copy
semantics over no-caller-copy (callee-copy-on-write) semantics.  But
getIndirect(x) actually means that x is passed by pointer at the IR
level but (at least on all other targets I looked at) directly at the
ABI level.  getIndirect(x, false) selects a pointer to a caller-made
copy, which is what SystemZ was aiming for.

This fixes a miscompilation of c-index-test.  Structure arguments were being
passed by pointer, but no copy was being made, so a write in the callee
stomped over a caller's local variable.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@196370 91177308-0d34-0410-b5e6-96231b3b80d8
do not warn about unknown pragmas in modes that do not handle them (pr9537)

And refactor to have just one place in code that sets up the empty
pragma handlers.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@196372 91177308-0d34-0410-b5e6-96231b3b80d8