make some variables unsigned

make some variables unsigned

these places define char arrays containing values greater than 0x80 which
doesn't fit in an 8 bit signed char, but does fit in an unsigned one.

gas/ChangeLog:

2016-03-31  Trevor Saunders  <tbsaunde+binutils@tbsaunde.org>

	* config/tc-aarch64.c (aarch64_handle_align): Make the type of some
	variables unsigned char[].
	* config/tc-alpha.c (alpha_handle_align): Likewise.
	* config/tc-arm.c (arm_handle_align): Likewise.
	* config/tc-z80.c: Likewise.