pru: Enable section anchoring by default

pru: Enable section anchoring by default

Loading an arbitrary constant address in a register is expensive for
PRU.  So enable section anchoring by default to utilize the unsigned
byte constant offset operand of load/store instructions.

gcc/ChangeLog:

	* common/config/pru/pru-common.cc
	(TARGET_OPTION_OPTIMIZATION_TABLE): New definition.
	* config/pru/pru.cc (TARGET_MIN_ANCHOR_OFFSET): Set minimal
	anchor offset.
	(TARGET_MAX_ANCHOR_OFFSET): Set maximum anchor offset.

gcc/testsuite/ChangeLog:

	* gcc.target/pru/section-anchors-1.c: New test.
	* gcc.target/pru/section-anchors-2.c: New test.

Signed-off-by: Dimitar Dimitrov <dimitar@dinux.eu>