[PATCH] [mips] Defer va_arg expansion to the backend.

[Reid Kleckner]

Looks good to me, as a drive by.

================
Comment at: test/CodeGen/mips-vaarg.c:6
@@ +5,3 @@
+
+int foo (int a, ...)
+{
----------------
Seems light.  How about doing CHECK-LABEL on 'define i32 @foo' and looking for call @llvm.va_start and end?

http://reviews.llvm.org/D4742