Add support to readelf for displaying gnu attributes in architectures not known to...

Add support to readelf for displaying gnu attributes in architectures not known to support them.

	* readelf.c (display_tag_value): Use an explicit signed type for
	the tag parameter.
	(display_gnu_attributes): Use an unsigned integer type for
	attribute tags.
	(display_power_gnu_attribute): Likewise.
	(display_s390_gnu_attribute): Likewise.
	(display_sparc_hwcaps): Likewise.
	(display_sparc_hwcaps2): Likewise.
	(display_sparc_gnu_attribute): Likewise.
	(display_mips_gnu_attribute): Likewise.
	(display_tic6x_attribute): Likewise.
	(display_raw_attribute): Likewise.
	(process_attributes): Likewise.
	(process_arm_specific): Delete redundant function.
	(process_power_specific): Likewise.
	(process_s390_specific): Likewise.
	(process_sparc_specific): Likewise.
	(process_tic6x_specific): Likewise.
	(process_msp430x_specific): Likewise.
	(display_public_gnu_attributes): New function.  Displays known
	information about an unknown gnu attribute.
	(display_generic_attribute): New function.  Calls
	display_tag_value for non-nul tags.
	(process_arch_specific): Call process_attributes even for
	architectures not known to specifically support gnu attributes.