arc: Detect usage of illegal double register pairs

arc: Detect usage of illegal double register pairs

ARC can use odd-even double register pairs in some selected
instructions. Although the GNU assembler doesn't allow even-odd
registers to be used, there may be cases when the disassembler is
presented with such situation.  This patch add a test and detects such
cases.

opcodes/
2020-07-14  Claudiu Zissulescu  <claziss@gmail.com>

	* arc-dis.c (print_insn_arc): Detect and emit a warning when a
	faulty double register pair is detected.

binutils/
2020-07-14  Claudiu Zissulescu  <claziss@gmail.com>

	* testsuite/binutils-all/arc/double_regs.s: New test.
	* testsuite/binutils-all/arc/objdump.exp: Add the above test.

Signed-off-by: Claudiu Zissulescu <claziss@gmail.com>