compiler: preserve nointerface property when inlining methods

When an inline function (with body) is imported from another package,
make that the "nointerface" property (if set) is preserved.

Fixes golang/go#30862.

Change-Id: I8fca667b1373c066053463c0b9a9dcf3c2260d65
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/167742
Reviewed-by: Ian Lance Taylor <iant@golang.org>
1 file changed