[arm] PR target/88469 fix incorrect argument passing with 64-bit bitfields

[arm] PR target/88469 fix incorrect argument passing with 64-bit bitfields

Unfortunately another PCS bug has come to light with the layout of
structs whose alignment is dominated by a 64-bit bitfield element.
Such fields in the type list appear to have alignment 1, but in
reality, for the purposes of alignment of the underlying structure,
the alignment is derived from the underlying bitfield's type.  We've
been getting this wrong since support for over-aligned record types
was added several releases back.  Worse still, the existing code may
generate unaligned memory accesses that may fault on some versions of
the architecture.

I've taken the opportunity to add a few more tests that check the
passing arguments with overalignment in the PCS.  Looking through the
existing tests it looked like they were really only checking
self-consistency and not the precise location of the arguments.

PR target/88469

gcc:
	* config/arm/arm.c (arm_needs_doubleword_align): Return 2 if a record's
	alignment is dominated by a bitfield with 64-bit aligned base type.
	(arm_function_arg): Emit a warning if the alignment has changed since
	earlier GCC releases.
	(arm_function_arg_boundary): Likewise.
	(arm_setup_incoming_varargs): Likewise.

gcc/testsuite:
	* gcc.target/arm/aapcs/bitfield1.c: New test.
	* gcc.target/arm/aapcs/overalign_rec1.c: New test.
	* gcc.target/arm/aapcs/overalign_rec2.c: New test.
	* gcc.target/arm/aapcs/overalign_rec3.c: New test.

From-SVN: r268151