libgccjit: Remove attributes declaration duplication

	gcc/c-family/Changelog:

		* gcc/c-family/c-common.h: Reexport c_common_gnu_attribute_table

	gcc/jit/Changelog:

		* gcc/jit/dummy-frontend.cc: Remove attributes duplication

Signed-off-by: Guillaume Gomez <guillaume1.gomez@gmail.com>

Author: GuillaumeGomez