Update stdarch submodule

This mainly fixes the critical issue of aarch64 store intrinsics
overwriting additional memory, see
https://github.com/rust-lang/stdarch/issues/1220

Other changes:
* aarch64/armv7: additional vld1/vst1 intrinsics + perf fixes for existing ones
* armv7: Make FMA work with vfpv4
* Non-visible changes to the testing framework

diff --git a/library/stdarch b/library/stdarch
index 89b0e355bc3cff5cddec2290c84f36eb3a026aad..5fdbc476afc81a789806697fc4a2d9d19b8c9993 160000 (submodule)
--- a/library/stdarch
+++ b/library/stdarch
@@ -1 +1 @@
-Subproject commit 89b0e355bc3cff5cddec2290c84f36eb3a026aad
+Subproject commit 5fdbc476afc81a789806697fc4a2d9d19b8c9993