scripts/faddr2line: fix CROSS_COMPILE unset error

commit 4cc90b4cc3d4955f79eae4f7f9d64e67e17b468e upstream.

faddr2line hit var unbound error when CROSS_COMPILE isn't set since
nounset option is set in bash script.

Link: http://lkml.kernel.org/r/20171206013022.GA83929@sofia
Fixes: 95a879825419 ("scripts/faddr2line: extend usage on generic arch")
Signed-off-by: Liu Changcheng <[email protected]>
Reported-by: Richard Weinberger <[email protected]>
Reviewed-by: Richard Weinberger <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Philippe Ombredanne <[email protected]>
Cc: NeilBrown <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: LiucIntel

Diff for: scripts/faddr2line

@@ -44,10 +44,10 @@
 set -o errexit
 set -o nounset
 
-READELF="${CROSS_COMPILE}readelf"
-ADDR2LINE="${CROSS_COMPILE}addr2line"
-SIZE="${CROSS_COMPILE}size"
-NM="${CROSS_COMPILE}nm"
+READELF="${CROSS_COMPILE:-}readelf"
+ADDR2LINE="${CROSS_COMPILE:-}addr2line"
+SIZE="${CROSS_COMPILE:-}size"
+NM="${CROSS_COMPILE:-}nm"
 
 command -v awk >/dev/null 2>&1 || die "awk isn't installed"
 command -v ${READELF} >/dev/null 2>&1 || die "readelf isn't installed"