S/390: Fix the vec_xl / vec_xst style builtins

S/390: Fix the vec_xl / vec_xst style builtins

This patch fixes several problems with the vec_xl/vec_xst builtins:

- vec_xl/vec_xst needs to use the alignment of the scalar memory
  operand for the vector type reference. This is required to emit the
  proper vl/vst alignment hints.
- vec_xl / vec_xld2 / vec_xlw4 should accept const pointer source operands
- vec_xlw4 / vec_xstw4 needs to accept float memory operands

gcc/ChangeLog:

2019-02-07  Andreas Krebbel  <krebbel@linux.ibm.com>

	* config/s390/s390-builtin-types.def: Add new types.
	* config/s390/s390-builtins.def: (s390_vec_xl, s390_vec_xld2)
	(s390_vec_xlw4): Make the memory operand into a const pointer.
	(s390_vec_xld2, s390_vec_xlw4): Add a variant for single precision
	float.
	* config/s390/s390-c.c (s390_expand_overloaded_builtin): Generate
	a new vector type with the alignment of the scalar memory operand.

gcc/testsuite/ChangeLog:

2019-02-07  Andreas Krebbel  <krebbel@linux.ibm.com>

	* gcc.target/s390/zvector/xl-xst-align-1.c: New test.
	* gcc.target/s390/zvector/xl-xst-align-2.c: New test.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@268651 138bc75d-0d04-0410-961f-82ee72b054a4