[recipes] Add toolchain version to extra_cflags.

In compile recipes, add a dummy define (e.g.
-DDUMMY_clang_linux_version=42) to the compiler flags so that ninja will
recompile from scratch when the toolchain changes.

Bug: skia:7720
Change-Id: I9a330b21af364b3aa6a1eebbe6ac2022cfa82fdc
Reviewed-on: https://skia-review.googlesource.com/115160
Reviewed-by: Eric Boren <borenet@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Ben Wagner <benjaminwagner@google.com>
69 files changed