This is backported partially from 2.20 branch

 http://sourceware.org/ml/binutils-cvs/2009-10/msg00173.html

 -Khem

 Index: binutils-2.20/gas/as.h

 ===================================================================

 --- binutils-2.20.orig/gas/as.h	2009-10-22 00:27:08.700469349 -0700

 +++ binutils-2.20/gas/as.h	2009-10-22 00:28:04.068416318 -0700

 @@ -238,7 +238,7 @@ typedef addressT valueT;

  #define know(p) gas_assert(p)	/* Verify our assumptions!  */

  #endif /* not yet defined */

  #else

 -#define know(p)			/* know() checks are no-op.ed  */

 +#define know(p) do {} while (0)	/* know() checks are no-op.ed  */

  #endif

  /* input_scrub.c */