middle-end: Remove all GCC's uses of ENUM_BITFIELD. [PR125507]

GCC requires C++14, which supports enum bitfield so ENUM_BITFIELD
is removed in GCC.

Bootstrapped and regtested on x86_64-pc-linux-gnu.

	PR middle-end/125507

contrib/ChangeLog:

	* filter_params.py (filter_src): Remove ENUM_BITFIELD.
	(FilteringTests): Ditto.

gcc/ChangeLog:

	* gengtype-lex.l: Remove ENUM_BITFIELD.
	* real.h (struct real_value): Ditto.

Signed-off-by: Kael Andrew Franco <kaelfandrew@gmail.com>