S/390: Add support for section anchors

S/390: Add support for section anchors

gcc/ChangeLog:

2018-12-03  Ilya Leoshkevich  <iii@linux.ibm.com>

	* common/config/s390/s390-common.c (s390_option_init_struct):
	Use section anchors by default.
	* config/s390/s390.c (s390_check_symref_alignment): Handle
	anchors.
	(TARGET_MAX_ANCHOR_OFFSET): Use short displacement.
	* output.h (assemble_align): Pass `align' as unsigned int, so
	that the value 0x80000000, which corresponds to `aligned(1 <<
	28)', would pass the `align > BITS_PER_UNIT' check.
	* varasm.c (assemble_align): Likewise.

gcc/testsuite/ChangeLog:

2018-12-03  Ilya Leoshkevich  <iii@linux.ibm.com>

	* gcc.target/s390/nodatarel-1.c: Expect .LANCHOR0@GOTENT instead
	of a@GOTENT.
	* gcc.target/s390/section-anchors.c: New test.
	* gcc.target/s390/section-anchors2.c: New test.
	* gcc.target/s390/section-anchors3.c: New test.

From-SVN: r266741