You asked about the alignment stuff for isa_defs.h.
Ok, here goes (the added stuff is #ifdef'ed "NEW"):
Note: I'm not married to the names, just the idea.

/*
 * Copyright (c) 1993-1994, by Sun Microsystems, Inc.
 */

#ifndef	_SYS_ISA_DEFS_H
#define	_SYS_ISA_DEFS_H

#pragma ident	"@(#)isa_defs.h	1.5	94/07/29 SMI"

/*
 * This header file serves to group a set of well known defines and to
 * set these for each instruction set architecture.  These defines may
 * be divided into two groups;
 *
 * 	isa_defs.h	characteristics of the processor, and
 * 	impl_defs.h	implementation choices for Solaris on a processor.
 *
 * Processor Characteristics:
 *
 * _LITTLE_ENDIAN / _BIG_ENDIAN:
 *	The natural byte order of the processor.  A pointer to an int points
 *	to the least/most significant byte of that int.
 *
 * _STACK_GROWS_UPWARD / _STACK_GROWS_DOWNWARD:
 *	The processor specific direction of stack growth.  A push onto the
 *	stack increases/decreases the stack pointer, so it stores data at
 *	successively higher/lower addresses.  (Stackless machines ignored
 *	without regrets).
 *
 * _LONG_LONG_HTOL / _LONG_LONG_LTOH:
 *	A pointer to a long long points to the most/least significant long
 *	within that long long.
 *
 * _BIT_FIELDS_HTOL / _BIT_FIELDS_LTOH:
 *	The C compiler assigns bit fields from the high/low to the low/high end
 *	of an int (most to least significant vs. least to most significant).
 *
 * _IEEE_754:
 *	The processor (or supported implementations of the processor)
 *	supports the ieee-754 floating point standard.  No other floating
 *	point standards are supported (or significant).  Any other supported
 *	floating point formats are expected to be cased on the ISA processor
 *	symbol.
 *
 * _CHAR_IS_UNSIGNED / _CHAR_IS_SIGNED:
 *	The C Compiler implements objects of type `char' as `unsigned' or
 *	`signed' respectively.  This is really an implementation choice of
 *	the compiler writer, but it is specified in the ABI and tends to
 *	be uniform across compilers for an instruction set architecture.
 *	Hence, it has the properties of a processor characteristic.
 *
#ifdef NEW
 * _CHAR_ALIGNMENT / _SHORT_ALIGNMENT / _INT_ALIGNMENT / _LONG_ALIGNMENT /
 * _LONG_LONG_ALIGNMENT / _DOUBLE_ALIGNMENT / _LONG_DOUBLE_ALIGNMENT /
 * _POINTER_ALIGNMENT:
 *	The ABI defined alignment requirements of each of the primitive
 *	object types.  Some, if not all, may be hardware requirements as
 * 	well.  The values are expressed in "byte-alignment" units.
 *
 * _ALIGNMENT_REQUIRED:
 *	True or false (1 or 0) whether or not the hardware requires the ABI
 *	alignment.
 *	
#endif NEW
 */

#ifdef	__cplusplus
extern "C" {
#endif


/*
 * The following set of definitions characterize the Solaris on Intel systems.
 *
 * The feature test macro __i386 is generic for all processors implementing
 * the Intel 386 instruction set or a superset of it.  Specifically, this
 * includes all members of the 386, 486, and Pentium family of processors.
 */
#if defined(__i386) || defined(i386)

/*
 * Make sure that the ANSI-C "politically correct" symbol is defined.
 */
#if !defined(__i386)
#define	__i386
#endif

/*
 * Define the appropriate "processor characteristics"
 */
#define	_LITTLE_ENDIAN
#define	_STACK_GROWS_DOWNWARD
#define	_LONG_LONG_LTOH
#define	_BIT_FIELDS_LTOH
#define	_IEEE_754
#define	_CHAR_IS_SIGNED
#ifdef NEW
#define	_CHAR_ALIGNMENT		1
#define	_SHORT_ALIGNMENT	2
#define	_INT_ALIGNMENT		4
#define	_LONG_ALIGNMENT		4
#define	_LONG_LONG_ALIGNMENT	4
#define	_DOUBLE_ALIGNMENT	4
#define	_LONG_DOUBLE_ALIGNMENT	4
#define	_POINTER_ALIGNMENT	4
#define	_ALIGNMENT_REQUIRED	0
#endif NEW


/*
 * The following set of definitions characterize the Solaris on PowerPC systems.
 *
 * The feature test macro __ppc is generic for all processors implementing
 * the PowerPC instruction set or a superset of it.  Specifically, this
 * includes all members of the 601, 603, 604, and 620 family of processors.
 */
#elif defined(__ppc)

/*
 * Define the appropriate "processor characteristics"
 */
#define	_LITTLE_ENDIAN
#define	_STACK_GROWS_DOWNWARD
#define	_LONG_LONG_LTOH
#define	_BIT_FIELDS_LTOH
#define	_IEEE_754
#define	_CHAR_IS_SIGNED
#ifdef NEW
#define	_CHAR_ALIGNMENT		1
#define	_SHORT_ALIGNMENT	2
#define	_INT_ALIGNMENT		4
#define	_LONG_ALIGNMENT		4
#define	_LONG_LONG_ALIGNMENT	8
#define	_DOUBLE_ALIGNMENT	8
#define	_LONG_DOUBLE_ALIGNMENT	16
#define	_POINTER_ALIGNMENT	4
#define	_ALIGNMENT_REQUIRED	1
#endif NEW


/*
 * The following set of definitions characterize the Solaris on SPARC system.
 *
 * The flag __sparc is only guaranteed to indicate SPARC processors version 8
 * or earlier.
 */
#elif defined(__sparc) || defined(sparc)

/*
 * Make sure that the ANSI-C "politically correct" symbol is defined.
 */
#if !defined(__sparc)
#define	__sparc
#endif

/*
 * Define the appropriate "processor characteristics"
 */
#define	_BIG_ENDIAN
#define	_STACK_GROWS_DOWNWARD
#define	_LONG_LONG_HTOL
#define	_BIT_FIELDS_HTOL
#define	_IEEE_754
#define	_CHAR_IS_SIGNED
#ifdef NEW
#define	_CHAR_ALIGNMENT		1
#define	_SHORT_ALIGNMENT	2
#define	_INT_ALIGNMENT		4
#define	_LONG_ALIGNMENT		4
#define	_LONG_LONG_ALIGNMENT	8
#define	_DOUBLE_ALIGNMENT	8
#define	_LONG_DOUBLE_ALIGNMENT	8
#define	_POINTER_ALIGNMENT	4
#define	_ALIGNMENT_REQUIRED	1
#endif NEW


/*
 * #error is strictly ansi-C, but works as well as anything for K&R systems.
 */
#else
#error ISA not supported
#endif

#ifdef	__cplusplus
}
#endif

#endif	/* _SYS_ISA_DEFS_H */