Update compiler-builtins

tamird · tamird · commit 49492cb861cc · 2017-09-13T22:55:46.000-04:00
Picks up the removal of the rustbuild feature, which is still used
in our local shim, along with a comment update explaining the usage.
diff --git a/src/libcompiler_builtins b/src/libcompiler_builtins
@@ -1 +1 @@
-Subproject commit 38ffaf97aa418cc369ca0197a72a0b927cc0f622
+Subproject commit ef4951582f620c589cd9e18ec182538bf116bce3
