[arm] Further fixes for PR88469

[arm] Further fixes for PR88469

A bitfield that is exactly the same size as an integral type and
naturally aligned will have DECL_BIT_FIELD cleared.  So we need to
check DECL_BIT_FIELD_TYPE to be sure whether or not the underlying
type was declared with a bitfield declaration.

I've also added a test for bitfields that are based on overaligned types.

	PR target/88469
gcc:
	* config/arm/arm.c (arm_needs_double_word_align): Check
	DECL_BIT_FIELD_TYPE.

gcc/testsuite:
	* gcc.target/arm/aapcs/bitfield2.c: New test.
	* gcc.target/arm/aapcs/bitfield3.c: New test.

From-SVN: r268160