Add IR constructs for preallocated (inalloca replacement)

Add llvm.call.preallocated.{setup,arg} instrinsics.
Add "preallocated" operand bundle which takes a token produced by llvm.call.preallocated.setup.
Add "preallocated" parameter attribute, which is like byval but without the copy.

Verifier changes for these IR constructs.

See https://github.com/rnk/llvm-project/blob/call-setup-docs/llvm/docs/CallSetup.md

Subscribers: hiraditya, jdoerfert, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D74651

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -725,6 +725,8 @@ static uint64_t getAttrKindEncoding(Attribute::AttrKind Kind) {
     return bitc::ATTR_KIND_IMMARG;
   case Attribute::SanitizeMemTag:
     return bitc::ATTR_KIND_SANITIZE_MEMTAG;
+  case Attribute::Preallocated:
+    return bitc::ATTR_KIND_PREALLOCATED;
   case Attribute::EndAttrKinds:
     llvm_unreachable("Can not encode end-attribute kinds marker.");
   case Attribute::None: