Change the regex used to determine whether a file should be processed as
C source to include .c.inc and .h.inc extensions.

Signed-off-by: Matheus Ferst <matheus.ferst@eldorado.org.br>
Reviewed-by: Luis Pires <luis.pires@eldorado.org.br>
Message-Id: <20210520195142.941261-1-matheus.ferst@eldorado.org.br>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>