LLVM 12.0, 13.0 support
There is a mention in LLVM 12.0.0 Release Notes that "Added type parameter to the sret attribute..."
(see https://releases.llvm.org/12.0.0/docs/ReleaseNotes.html#changes-to-the-llvm-ir)
LLVM Language Reference Manual specifies the syntax byval(<ty>)
, sret(<ty>)
(see https://llvm.org/docs/LangRef.html#parameter-attributes)
These changes in the syntax of LLVM 12 and 13 are taken into account in this MR.