This patch adds support for compiling rest patterns present in slice patterns
(e.g. `[1, .., 2]`). 006t.original output from compiling match-slicepattern-slice-2.rs
for first 2 match arms:

...
  if (RUSTTMP.3.len > 1 && *NON_LVALUE_EXPR <RUSTTMP.3.data> == 1)
    {
      {
                struct () RUSTTMP.4;
        {
                    struct () RUSTTMP.5;
          {
           ..
          }
        }
        goto <D.139>;
      }
    }
  if ((RUSTTMP.3.len > 1 && *NON_LVALUE_EXPR <RUSTTMP.3.data> == 0) && *(RUSTTMP.3.data + (sizetype) (RUSTTMP.3.len + 18446744073709551615) * 4) == 0)
    {
      {
                struct () RUSTTMP.6;
        {
                    struct () RUSTTMP.7;
          {
          }
        }
        goto <D.139>;
      }
    }
...

gcc/rust/ChangeLog:

	* hir/tree/rust-hir-pattern.h: Add SlicePatternItems base class and
	SlicePatternItemsNoRest/SlicePatternItemsHasRest derived classes.
	Update SlicePattern to hold patterns using the new classes.
	* hir/tree/rust-hir-full-decls.h: Declare new classes.
	* hir/tree/rust-hir.cc: Add visits for new classes.
	* hir/tree/rust-hir-visitor.h: Add visits for new classes.
	* hir/tree/rust-hir-visitor.cc: Implement visits for new classes.
	* hir/rust-hir-dump.h: Add visits for new classes.
	* hir/rust-hir-dump.cc: Implement Dump::visit for new classes.
	* hir/rust-ast-lower-base.h: Declare new lower_slice_pattern_no_rest/has_rest
	methods.
	* hir/rust-ast-lower-base.cc: Implement lower_slice_pattern_no_rest/has_rest
	to lower AST slice pattern items to HIR.
	* hir/rust-ast-lower-pattern.cc: Update ASTLoweringPattern::visit for
	SlicePattern to use new lowering methods.
	* backend/rust-compile-pattern.cc: Update CompilePatternCheckExpr::visit
	and CompilePatternBindings::visit for SlicePattern to handle
	SlicePatternItemsNoRest/HasRest.
	* checks/errors/borrowck/rust-bir-builder-pattern.cc: Update
	PatternBindingBuilder::visit for SlicePattern to iterate members correctly.
	* checks/errors/borrowck/rust-bir-builder-struct.h: Add visits for new
	classes.
	* checks/errors/borrowck/rust-function-collector.h: Add visits for new
	classes.
	* checks/errors/rust-const-checker.h: Add visits for new classes.
	* checks/errors/rust-const-checker.cc: Implement empty visits for new classes.
	* checks/errors/rust-hir-pattern-analysis.h: Add visits for new classes.
	* checks/errors/rust-hir-pattern-analysis.cc: Implement empty visits for new
	classes.
	* checks/errors/rust-unsafe-checker.h: Add visits for new classes.
	* checks/errors/rust-unsafe-checker.cc: Implement empty visits for new
	classes.
	* typecheck/rust-hir-type-check-pattern.cc: Update TypeCheckPattern::visit
	for SlicePattern to handle SlicePatternItemsNoRest/HasRest.

gcc/testsuite/ChangeLog:

	* rust/compile/slice_rest_pattern.rs: Removed -fsyntax-only.

Signed-off-by: Yap Zhi Heng <[email protected]>