The code sequence for large-offset floating-point stores
includes adding the base pointer to r11.  Make sure we
can interpret that instruction correctly.

Fixes build.

Fixes #15440

Change-Id: I7fe5a4a57e08682967052bf77c54e0ec47fcb53e
Reviewed-on: https://go-review.googlesource.com/22440Reviewed-by: Michael Hudson-Doyle <michael.hudson@canonical.com>