Auto merge of rust-lang#52431 - semarie:compiler-builtins, r=alexcrichton

bors · bors · commit 166795dda66c · 2018-07-18T22:15:46.000Z
update compiler-builtins for openbsd import rust-lang/compiler-builtins/pull/249 in rust main line. it solves an issue on OpenBSD with building of `librsvg`.
diff --git a/src/libcompiler_builtins b/src/libcompiler_builtins
@@ -1 +1 @@
-Subproject commit 86bf357a14cacb4a4169455e729d409b5ecc1da0
+Subproject commit b4a3645cfe102a100b6ebecbe76df37bc957eda8
