crossgcc: close stdin when search_tool() execute programs.

bzip2 --version |grep -c will wait for input on stdin. ./buildgcc will hang because of this.
Add `cat /dev/null |` close the stdin.

Change-Id: I2a8b08a4d90ca7a89705923d5b68ba6ac13f29b3
Signed-off-by: Alexander Couzens <lynxis@fe80.eu>
Reviewed-on: http://review.coreboot.org/9605
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

util/crossgcc/buildgcc

@@ -108,7 +108,7 @@ searchtool()
 	fi
 	for i in "$1" "g$1" "gnu$1"; do
 		if test -x "`which $i 2>/dev/null`"; then
-			if test `$i --version 2>&1 |grep -c "$search"` \
+			if test `cat /dev/null | $i --version 2>&1 |grep -c "$search"` \
 			    -gt 0; then
 				echo $i
 				return