scripts/gdb: If not building expat for gdb, disable

--with-expat=yes is unconditionally passed to the gdb configure
stage, instead of respecting the ${do_expat} decision.

Disable if not needed. Prevents error building canadian cross;

configure: error: expat is missing or unusable

Where configure stage fails to find expat on the host compiler.

Signed-off-by: "David Holsgrove" <david.holsgrove@xilinx.com>
Signed-off-by: Bryan Hundven <bryanhundven@gmail.com>
Message-Id: <4c4410a2a8aab24a29c5.1349244128@localhost.localdomain>
PatchWork-Id: 188711

 --- a/bfd/elf32-arm.c

 +++ b/bfd/elf32-arm.c

 @@ -12408,7 +12408,8 @@ elf32_arm_check_relocs (bfd *abfd, struc

  	  /* If the symbol is a function that doesn't bind locally,

  	     this relocation will need a PLT entry.  */

 -	  root_plt->refcount += 1;

 +	  if (root_plt->refcount != -1)

 +	    root_plt->refcount += 1;

  	  if (!call_reloc_p)

  	    arm_plt->noncall_refcount++;