[BACKPORT] Fix -Wstring-concatenation warnings in clang 12 Change-Id: Ic09346b6079e6f316c28e03ddb02f12b4af8a38d Reviewed-on: https://skia-review.googlesource.com/c/skia/+/312482 Reviewed-by: Mike Klein <[email protected]> Commit-Queue: Brian Salomon <[email protected]>