d: Merge upstream dmd, druntime e4f8919591, phobos 3ad507b51.

D front-end changes:

    - Import dmd v2.101.0-beta.1.
    - Add predefined version `D_Optimized' when compiling with `-O'.
    - Shortened method syntax (DIP1043) is now enabled by default.
    - Array literals assigned to `scope' array variables are now
      allocated on the stack.
    - Implement `@system' variables (DIP1035), available behind the
      preview feature flag `-fpreview=systemvariables'.

D runtime changes:

    - Import druntime v2.101.0-beta.1.

Phobos changes:

    - Import phobos v2.101.0-beta.1.
    - Added `std.typecons.SafeRefCounted', that can be used in `@safe'
      code with `-fpreview=dip1000'.

gcc/d/ChangeLog:

	* d-attribs.cc (apply_user_attributes): Update for new front-end
	interface.
	* d-builtins.cc (d_init_versions): Predefine `D_Optimized' with
	compiling with optimizations enabled.
	* d-lang.cc (d_handle_option): Update for new front-end interface.
	Handle new option `-fpreview=systemvariables'.
	* dmd/MERGE: Merge upstream dmd e4f8919591.
	* dmd/VERSION: Bump version to v2.101.0-beta.1.
	* expr.cc (ExprVisitor::visit (AssignExp *)): Treat construction of
	static arrays from a call expression as a simple assignment.
	(ExprVisitor::visit (ArrayLiteralExp *)): Handle array literals with
	`scope' storage.
	* gdc.texi: Update documentation of `-fpreview=' options.
	* lang.opt (fpreview=shortenedmethods): Remove.
	(fpreview=systemvariables):  New option.

libphobos/ChangeLog:

	* libdruntime/MERGE: Merge upstream druntime e4f8919591.
	* src/MERGE: Merge upstream phobos 3ad507b51.

gcc/testsuite/ChangeLog:

	* gdc.dg/simd19630.d: Move tests with errors to ...
	* gdc.dg/simd19630b.d: ... here.  New test.
	* gdc.dg/simd19630c.d: New test.
	* gdc.dg/simd_ctfe.d: Removed.
	* gdc.dg/simd18867.d: New test.
	* gdc.dg/simd19788.d: New test.
	* gdc.dg/simd21469.d: New test.
	* gdc.dg/simd21672.d: New test.
	* gdc.dg/simd23077.d: New test.
	* gdc.dg/simd23084.d: New test.
	* gdc.dg/simd23085.d: New test.
	* gdc.dg/torture/simd19632.d: New test.
	* gdc.dg/torture/simd20041.d: New test.
	* gdc.dg/torture/simd21673.d: New test.
	* gdc.dg/torture/simd21676.d: New test.
	* gdc.dg/torture/simd22438.d: New test.
	* gdc.dg/torture/simd23009.d: New test.
	* gdc.dg/torture/simd23077.d: New test.
	* gdc.dg/torture/simd8.d: New test.
	* gdc.dg/torture/simd9.d: New test.
	* gdc.dg/torture/simd_prefetch.d: New test.