Pull in a wasm fix from LLVM upstream

This pulls in a fix for https://bugs.llvm.org/show_bug.cgi?id=36564 which has
already landed in upstream LLVM and should...

Closes rust-lang-nursery/rust-wasm#168

diff --git a/src/llvm b/src/llvm
index b6c1a03fb498f6c03d1cbfd4404223a046f8c3b2..fd7dd99edf371ac502ae4e70288c027f6692ace0 160000 (submodule)
--- a/src/llvm
+++ b/src/llvm
@@ -1 +1 @@
-Subproject commit b6c1a03fb498f6c03d1cbfd4404223a046f8c3b2
+Subproject commit fd7dd99edf371ac502ae4e70288c027f6692ace0