Add a fBuiltin flag to FunctionDefinition.

This is useful because we can clone FunctionDefinitions without cloning
the matching FunctionDeclaration. The FunctionDeclaration will remain a
builtin, but the definition should be a malleable clone.

Change-Id: Icfc1e0855fb8fcd6914a5d657f5098986fcf19ea
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/328396
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
5 files changed