d: Merge upstream dmd 60bfa0ee7, druntime 94bd5bcb, phobos 3a1cd9a01.

D front-end changes:

    - Import dmd v2.100.0.
    - Add bit fields to D, enabled via the -fpreview=bitfields switch.
    - Removed the -ftransition=markdown and -frevert=markdown switches.
    - Added new trait `__traits(classInstanceAlignment)' to provide the
      required data alignment for classes.
    - The check for `pragma(crt_constructor)' and `pragma(crt_destructor)'
      linkage has been relaxed to allow all `void()' signatures.
    - ImportC parser now recognizes the `typeof(...)' operator.

D runtime changes:

    - Import druntime v2.100.0.

Phobos changes:

    - Import phobos v2.100.0.
    - To comply with dip1000, `std.socket.Socket` methods now accept only
      `scope' arrays.
    - The `fill', `alignSize', `align2', and `align4' methods of
      `std.outbuffer.OutBuffer' have been extended to allow specifying a custom
      value when pre-filling or padding the buffer.

gcc/d/ChangeLog:

	* dmd/MERGE: Merge upstream dmd 60bfa0ee7.
	* dmd/VERSION: Update version to v2.100.0.
	* d-builtins.cc (d_init_versions): Update for new front-end interface.
	* d-codegen.cc (d_decl_context): Use resolvedLinkage to get
	declaration linkage.
	(build_struct_literal): Track offset in bits.
	* d-gimplify.cc (d_gimplify_modify_expr): Check both operands for a
	bit-field reference.
	* d-lang.cc (d_handle_option): Handle -fpreview=bitfields, remove
	-frevert=markdown and -ftransition=vmarkdown.
	(d_post_options): Set flag_rtti and flag_exceptions if -fno-druntime
	was seen on command-line.
	(d_parse_file): Update for new front-end interface.
	(d_type_promotes_to): Use resolvedLinkage to get declaration linkage.
	* decl.cc (make_thunk): Likewise.
	* expr.cc (ExprVisitor::visit (CatAssignExp *)): Remove lowering for
	appending of an element or array to another array.
	* lang.opt (fpreview=bitfields): New option.
	(frevert=markdown): Remove.
	(ftransition=vmarkdown): Remove.
	* types.cc (layout_aggregate_members): Ignore anonymous fields in
	total count.

libphobos/ChangeLog:

	* libdruntime/MERGE: Merge upstream druntime 94bd5bcb.
	* libdruntime/Makefile.am (ALL_DRUNTIME_INSTALL_DSOURCES): Add
	$(DRUNTIME_DSOURCES_ELF).
	(ALL_DRUNTIME_SOURCES): Likewise.
	(DRUNTIME_DSOURCES_ELF): New variable.
	* libdruntime/Makefile.in: Regenerate.
	* src/MERGE: Merge upstream phobos 3a1cd9a01.
	* testsuite/libphobos.init_fini/custom_gc.d: Update test.