Add __builtin_speculation_safe_value

Add __builtin_speculation_safe_value

This patch defines a new intrinsic function
__builtin_speculation_safe_value.  A generic default implementation is
defined which will attempt to use the backend pattern
"speculation_safe_barrier".  If this pattern is not defined, or if it
is not available, then the compiler will emit a warning, but
compilation will continue.

Note that the test spec-barrier-1.c will currently fail on all
targets.  This is deliberate, the failure will go away when
appropriate action is taken for each target backend.

gcc:
	* builtin-types.def (BT_FN_PTR_PTR_VAR): New function type.
	(BT_FN_I1_I1_VAR, BT_FN_I2_I2_VAR, BT_FN_I4_I4_VAR): Likewise.
	(BT_FN_I8_I8_VAR, BT_FN_I16_I16_VAR): Likewise.
	* builtin-attrs.def (ATTR_NOVOPS_NOTHROW_LEAF_LIST): New attribute
	list.
	* builtins.def (BUILT_IN_SPECULATION_SAFE_VALUE_N): New builtin.
	(BUILT_IN_SPECULATION_SAFE_VALUE_PTR): New internal builtin.
	(BUILT_IN_SPECULATION_SAFE_VALUE_1): Likewise.
	(BUILT_IN_SPECULATION_SAFE_VALUE_2): Likewise.
	(BUILT_IN_SPECULATION_SAFE_VALUE_4): Likewise.
	(BUILT_IN_SPECULATION_SAFE_VALUE_8): Likewise.
	(BUILT_IN_SPECULATION_SAFE_VALUE_16): Likewise.
	* builtins.c (expand_speculation_safe_value): New function.
	(expand_builtin): Call it.
	* doc/cpp.texi: Document predefine __HAVE_SPECULATION_SAFE_VALUE.
	* doc/extend.texi: Document __builtin_speculation_safe_value.
	* doc/md.texi: Document "speculation_barrier" pattern.
	* doc/tm.texi.in: Pull in TARGET_SPECULATION_SAFE_VALUE and
	TARGET_HAVE_SPECULATION_SAFE_VALUE.
	* doc/tm.texi: Regenerated.
	* target.def (have_speculation_safe_value, speculation_safe_value): New
	hooks.
	* targhooks.c (default_have_speculation_safe_value): New function.
	(default_speculation_safe_value): New function.
	* targhooks.h (default_have_speculation_safe_value): Add prototype.
	(default_speculation_safe_value): Add prototype.

c-family:
	* c-common.c (speculation_safe_resolve_call): New function.
	(speculation_safe_resolve_params): New function.
	(speculation_safe_resolve_return): New function.
	(resolve_overloaded_builtin): Handle __builtin_speculation_safe_value.
	* c-cppbuiltin.c (c_cpp_builtins): Add pre-define for
	__HAVE_SPECULATION_SAFE_VALUE.

testsuite:
	* c-c++-common/spec-barrier-1.c: New test.
	* c-c++-common/spec-barrier-2.c: New test.
	* gcc.dg/spec-barrier-3.c: New test.

From-SVN: r263168