cmd/compile: inline multiplication corrupts an argument on arm [1.11 backport]

[gopherbot]

@josharian requested issue #28688 to be considered for backport to the next 1.11 minor release.

@gopherbot please open a backport tracking issue for 1.11. This is a compiler correctness bug.

[gopherbot]

Change https://golang.org/cl/151342 mentions this issue: [release-branch.go1.11] cmd/compile/internal/gc: OMUL should be evaluated when using soft-float

[gopherbot]

Closed by merging ba4638d to release-branch.go1.11.