Add the allocsize attribute to LLVM.

`allocsize` is a function attribute that allows users to request that
LLVM treat arbitrary functions as allocation functions.

This patch makes LLVM accept the `allocsize` attribute, and makes
`@llvm.objectsize` recognize said attribute.

The review for this was split into two patches for ease of reviewing:
D18974 and D14933. As promised on the revisions, I'm landing both
patches as a single commit.

Differential Revision: http://reviews.llvm.org/D14933

llvm-svn: 266032

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -164,6 +164,8 @@ static uint64_t getAttrKindEncoding(Attribute::AttrKind Kind) {
   switch (Kind) {
   case Attribute::Alignment:
     return bitc::ATTR_KIND_ALIGNMENT;
+  case Attribute::AllocSize:
+    return bitc::ATTR_KIND_ALLOC_SIZE;
   case Attribute::AlwaysInline:
     return bitc::ATTR_KIND_ALWAYS_INLINE;
   case Attribute::ArgMemOnly: