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

 --- uClibc-0.9.30.orig/extra/scripts/install_headers.sh	2008-10-10 15:50:38.000000000 +0200

 +++ uClibc-0.9.30/extra/scripts/install_headers.sh	2011-08-21 09:49:03.000000000 +0200

 @@ -33,7 +33,7 @@

  (

  # We must cd, or else we'll prepend "$1" to filenames!

  cd "$1" || exit 1

 -find ! -name '.' -a ! -path '*/.*' | sed -e 's/^\.\///' -e '/^config\//d' \

 +find . ! -name '.' -a ! -path '*/.*' | sed -e 's/^\.\///' -e '/^config\//d' \

  	-e '/^config$/d'

  ) | \

  (