Alters the existing targets to use a boot.cc file instead of the
existing early_boot.c.
The name was updated to reflect the fact that it now contains a
pw_boot_PostMain() hook which is after early boot.
C++ was selected over C to give more language flexibility.
Change-Id: I18ca0b8720bf083d4f644f1ca994e8fd7adc89b6
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/16702
Commit-Queue: Ewout van Bekkum <ewout@google.com>
Reviewed-by: Armando Montanez <amontanez@google.com>
Reviewed-by: Keir Mierle <keir@google.com>
