[ARC] Rework delegitimate_address hook

[ARC] Rework delegitimate_address hook

Delegitimize address is used to undo the obfuscating effect of PIC
addresses, returning the address in a way which is understood by the
compiler.  The old version of the hook was outdated, not beeing able
to recognize the current addresses generated by the ARC backend.

gcc/
2018-01-26  Claudiu Zissulescu  <claziss@synopsys.com>

	* config/arc/arc.c (arc_delegitimize_address_0): Refactored to
	recognize new pic like addresses.
	(arc_delegitimize_address): Clean up.

testsuite/
2018-01-26  Claudiu Zissulescu  <claziss@synopsys.com>

	* testsuite/gcc.target/arc/tdelegitimize_addr.c: New test.

From-SVN: r257084