cmd/compile, runtime, reflect: pointers to go:notinheap types must be stored indirectly in interfaces [1.15 backport]

[gopherbot]

@randall77 requested issue #42076 to be considered for backport to the next 1.15 minor release.

@gopherbot Please open a backport issue for 1.15.

[gopherbot]

Change https://golang.org/cl/265720 mentions this issue: cmd/compile, runtime: store pointers to go:notinheap types indirectly

[gopherbot]

Closed by merging 255afa2 to release-branch.go1.15.