cmd/compile: inline multiplication corrupts an argument on arm [1.10 backport]

[andybons]

Manually opening this due to gopherbot not tracking follow-up backport requests.

Issue #28688 is to be considered for backport to the next 1.10 minor release.

@josharian @milanknezevic

[gopherbot]

Change https://golang.org/cl/151343 mentions this issue: [release-branch.go1.10] cmd/compile/internal/gc: OMUL should be evaluated when using soft-float

[gopherbot]

Closed by merging d74e69c to release-branch.go1.10.

[gopherbot]

Change https://golang.org/cl/154297 mentions this issue: Revert "[release-branch.go1.10] cmd/compile/internal/gc: OMUL should be evaluated when using soft-float"