Fix the required args count for variadic blocks.

We were emitting calls to blocks as if all arguments were
required --- i.e. with signature (A,B,C,D,...) rather than
(A,B,...).  This patch fixes that and accounts for the
implicit block-context argument as a required argument.
In addition, this patch changes the function type under which
we call unprototyped functions on platforms like x86-64 that
guarantee compatibility of variadic functions with unprototyped
function types;  previously we would always call such functions
under the LLVM type T (...)*, but now we will call them under
the type T (A,B,C,D,...)*.  This last change should have no
material effect except for making the type conventions more
explicit;  it was a side-effect of the most convenient implementation.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@169588 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/TargetInfo.h b/lib/CodeGen/TargetInfo.h
index 913a1b0..bb50ce6 100644
--- a/lib/CodeGen/TargetInfo.h
+++ b/lib/CodeGen/TargetInfo.h
@@ -158,10 +158,13 @@
     ///   - the conventions are substantively different in how they pass
     ///     arguments, because in this case using the variadic convention
     ///     will lead to C99 violations.
-    /// It is not necessarily correct when arguments are passed in the
-    /// same way and some out-of-band information is passed for the
-    /// benefit of variadic callees, as is the case for x86-64.
-    /// In this case the ABI should be consulted.
+    ///
+    /// However, some platforms make the conventions identical except
+    /// for passing additional out-of-band information to a variadic
+    /// function: for example, x86-64 passes the number of SSE
+    /// arguments in %al.  On these platforms, it is desireable to
+    /// call unprototyped functions using the variadic convention so
+    /// that unprototyped calls to varargs functions still succeed.
     virtual bool isNoProtoCallVariadic(const CodeGen::CallArgList &args,
                                        const FunctionNoProtoType *fnType) const;
   };