Update LLVM

There's a number of goodies in this LLVM update:

* This contains a fix for https://llvm.org/bugs/show_bug.cgi?id=23957
  which should help us bootstrap farther on 32-bit MSVC targets.
* There is better support for writing multiple flavors of archives, allowing us
  to use the built-in LLVM support instead of the system `ar` on all current
  platforms of the compiler.
* A number of other minor bug fixes and performance improvements to unblock
  various other pieces of work.

Author: alexcrichton

src/llvm

@@ -1,4 +1,4 @@
 # If this file is modified, then llvm will be forcibly cleaned and then rebuilt.
 # The actual contents of this file do not matter, but to trigger a change on the
 # build bots then the contents should be changed so git updates the mtime.
-2015-06-16
+2015-06-30