Debug info: Support variadic functions.
Variadic functions have an unspecified parameter tag after the last
argument. In IR this is represented as an unspecified parameter in the
subroutine type.

Paired commit with CFE r202185.

rdar://problem/13690847

This re-applies r202184 + a bugfix in DwarfDebug's argument handling.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202188 91177308-0d34-0410-b5e6-96231b3b80d8
Store a DataLayout in Module.

Now that DataLayout is not a pass, store one in Module.

Since the C API expects to be able to get a char* to the datalayout description,
we have to keep a std::string somewhere. This patch keeps it in Module and also
uses it to represent modules without a DataLayout.

Once DataLayout is mandatory, we should probably move the string to DataLayout
itself since it won't be necessary anymore to represent the special case of a
module without a DataLayout.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202190 91177308-0d34-0410-b5e6-96231b3b80d8
Don't try to set a dummy DataLayout. It is parsed now.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202191 91177308-0d34-0410-b5e6-96231b3b80d8
Account for 128-bit integer operations in PPCCTRLoops

We need to abort the formation of counter-register-based loops where there are
128-bit integer operations that might become function calls.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202192 91177308-0d34-0410-b5e6-96231b3b80d8