[C11-atomic] Miscellaneous fixes 1/n

I've applied this patch to the C11-atomic branch to fix various
miscellaneous issues.

The largest part is implementing lvalue-to-rvalue conversions (which
have the effect of doing atomic loads), in all the various places in
the parser that need them.  I didn't particularly thoroughly check for
where these might be needed in ObjC syntax, so there's a sorry () for
use of _Atomic in ObjC until that is fixed, and didn't at all check in
OpenMP syntax, so there's another sorry () for that (it doesn't make
sense to update the OpenMP parsing on this branch anyway, given all
the new OpenMP 4 support since the branch was created).

Apart from that, the _Atomic (type-name) syntax is implemented.  The
tests for applying _Atomic qualifiers to function or array types are
fixed.  Lots of typos and formatting issues are fixed (but I'm sure
there are still more).  stdatomic.h is added to USER_H so it gets
installed.  __extension__ is added to macros in stdatomic.h.  Atomic
bit-fields are disallowed (this is implementation-defined in C11, but
we don't have anything to implement them).  typeof is made to remove
_Atomic qualifiers (and const qualifiers from _Atomic objects; it's
not entirely clear if use of const with the relevant macros is valid,
but it might be), when applied to expressions (as opposed to typeof
(type-name)).  The code generating atomic loads, atomic stores and the
more complicated sequences for atomic compound assignments is made to
put the sequence of statements inside a compound statement which forms
part of the returned expression - you can't just call add_stmt in
random places like the old code was doing, that will insert a
statement outside the current expression in the containing function
that won't be properly sequenced with respect to other parts of the
expression containing the atomic operation.

I put a hack in the C++ front end to disable checks on atomic
qualifiers so that libstdc++ builds - I think that if you want other
people to help on a development branch, it should be kept in a state
where it builds and tests cleanly.  However, I'm aiming specifically
to sort out the C front-end (and later stdatomic.h) issues, with a
view to getting the actual C11 support in shape and with adequate
testsuite coverage, so if that's ready on time I may propose it for
mainline without the attribute or C++ changes - as I understand it,
those are only needed for when targets start defining atomic types as
larger or more-aligned than the corresponding non-atomic types, not to
support the C11 features on the most common architectures.

2013-10-17  Joseph Myers  <joseph@codesourcery.com>

	* Makefile.in (USER_H): Add stdatomic.h.
	* ginclude/stdatomic.h: Fix formatting and typos.  Use correct
	types or predefined macros for atomic_* typedefs.  Use
	__extension__ in macro definitions.
	(enum memory_order): Specify values of enumeration constants using
	__ATOMIC_* predefined macros.
	* tree.c (build_common_tree_nodes): Fix typos.

c:
2013-10-17  Joseph Myers  <joseph@codesourcery.com>

	* c-decl.c (check_bitfield_type_and_width): Disallow atomic types.
	(grokdeclarator): Correct checks for atomic function or array
	types.
	* c-parser.c (c_parser_declspecs): Say "_Atomic" in comment.
	Handle _Atomic (type-name) syntax.  Adjust diagnostics for use of
	_Atomic outside C11 mode.  Call sorry for _Atomic with Objective-C
	or OpenMP.
	(c_parser_typeof_specifier): Remove const and _Atomic qualifiers
	from types of expressions with atomic type.
	(c_parser_direct_declarator_inner, c_parser_initializer)
	(c_parser_initelt, c_parser_statement_after_labels)
	(c_parser_switch_statement, c_parser_for_statement): Use
	convert_lvalue_to_rvalue.
	(c_parser_expr_no_commas): Don't handle atomic loads here.  Use
	convert_lvalue_to_rvalue.
	(c_parser_conditional_expression, c_parser_binary_expression)
	(c_parser_cast_expression, c_parser_unary_expression)
	(c_parser_postfix_expression)
	(c_parser_postfix_expression_after_primary, c_parser_expression):
	Use convert_lvalue_to_rvalue.
	(c_parser_expression_conv, c_parser_expr_list): Document
	conversion of lvalues to rvalues.  Use convert_lvalue_to_rvalue.
	(c_parser_objc_receiver, c_parser_array_notation): Use
	convert_lvalue_to_rvalue.
	* c-tree.h (ctsk_typeof): Adjust comment to mention use for
	_Atomic (type-name).
	(convert_lvalue_to_rvalue): Declare.
	* c-typeck.c (really_atomic_lvalue, convert_lvalue_to_rvalue): New
	functions.
	(build_modify_expr): Use really_atomic_lvalue.  Fix formatting.
	(build_asm_expr): Use convert_lvalue_to_rvalue.
	(build_atomic_assign): Fix formatting and typos.  Put sequence of
	statements inside a compound statement.
	(build_atomic_load): Remove function.  Merged into
	convert_lvalue_to_rvalue.

cp:
2013-10-17  Joseph Myers  <joseph@codesourcery.com>

	* typeck.c (at_least_as_qualified_p): Ignore differences in atomic
	qualifiers.

[C11-atomic] Miscellaneous fixes 1/n

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