Re: gas: macros nested too deep error

In commit fc2fcd4f5be3 I changed as as_fatal to as_bad, thinking that
was sufficient.  Revert that change because
  .macro r;r;r;.endm;r
with two recursive invocations in the body results in 2 to the power
max_macro_nest lines of gas output complaining about macro nesting.

	* input-scrub.c (input_scrub_include_sb): Revert last change.