pw_watch: Watch for .cpp and .hpp changes
pw_watch: Watch for .cpp and .hpp changes

Previously, pw watch would miss changes to files with .hpp or .cpp
extensions. Inside Pigweed, this doesn't matter, but for projects using
Pigweed, .cpp and .hpp are commmon extensions we should support.

Change-Id: Ia8bc6d0ef928fe24030f8644c8602c4974c6ad1b

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed