c-common.c (flag_abi_version): New variable.

	* c-common.c (flag_abi_version): New variable.
	* c-common.h (flag_abi_version): Declare it.
	* c-opts.c (missing_arg): Add -fabi-version.
	(c_common_decode_option): Process -fabi-version.
	* doc/invoke.texi (-fabi-version): Document it.
	(-Wabi): Add information about bit-fields in unions.

	* cp/class.c (layout_virtual_bases): Do not round the size of the
	type to a multiple of the alignment before laying out virtual bases.
	(layout_class_type): Correct handling of bit-fields that are wider
	than their type inside unions.  Round the size of the type to a
	even number of bytes when computing the size without virtual
	bases.
	* cp/cp-tree.h (abi_version_at_least): New macro.

	* g++.dg/abi/bitfield6.C: New test.
	* g++.dg/abi/bitfield7.C: New test.
	* g++.dg/abi/bitfield8.C: New test.
	* g++.dg/abi/vbase11.C: New test.

From-SVN: r57432