strub: avoid lto inlining

The strub builtins are not suited for cross-unit inlining, they should
only be inlined by the builtin expanders, if at all.  While testing on
sparc64, it occurred to me that, if libgcc was built with LTO enabled,
lto1 might inline them, and that would likely break things.  So, make
sure they're clearly marked as not inlinable.


for  libgcc/ChangeLog

	* strub.c (ATTRIBUTE_NOINLINE): New.
	(ATTRIBUTE_STRUB_CALLABLE): Add it.
	(__strub_dummy_force_no_leaf): Drop it.