add --dylib to fm

Change-Id: I1b75e703123d90712b001921d5b1e132238076fa
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/265823
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
1 file changed