21.8.12 Permitting inlining of functions with attributes

By default if a function has a target specific attribute attached to it, it will not be inlined. This behaviour can be overridden if the target defines the `FUNCTION_ATTRIBUTE_INLINABLE_P' macro. This macro takes one argument, a `DECL' describing the function. It should return non-zero if the function can be inlined, otherwise it should return 0.