Avoid setting or recording negative alignments when the target stores multiple octets...

Avoid setting or recording negative alignments when the target stores multiple octets in a single byte.

gas	* read.c (finish_bundle): Avoid recording a negative alignment.
	(do_align): Use unsigned values for n, len and max.  Only create
	a frag if the alignment requirement is greater than the minimum
	byte alignment.  Avoid recording a negative alignment.
	(s_align): Use unsigned values where appropriate.
	(bss_alloc): Use an unsigned value for the alignment.
	(sizeof_sleb128): Add a comment noting that we encode one octet
	per byte, regardless of the value of OCTETS_PER_BYTE_POWER.
	(emit_leb129_expr): Abort if the emitted encoding was longer than
	expected.
	* read.h (output_leb128): Update prototype.
	(sizeof_leb128): Update prototype.
	(bss_alloc): Update prototype.
	* write.c (record_alignment): Use an unsigned value for the
	alignment.  Do not record alignments less than the minimum
	alignment for a byte.
	* write.h (record_alignment): Update prototype.