install hooks: Interoperate with EAPI7

In EAPI7, the 'D' variable along with others doesn't have a trailing
slash anymore[1]. Let's use interoperable code here by removing any
trainling slash and then appending one manually.

[1] https://dev.gentoo.org/~mgorny/articles/the-ultimate-guide-to-eapi-7.html#d-ed-root-eroot-no-longer-have-a-trailing-slash

BUG=chromium:1011992
TEST=Emerge kernel with eapi7 package and make sure that .ko.debug and
vmlinux aren't scanned with llvm-readelf

Change-Id: I1984e8e67bf41db6ca78d6f4fe5bea9a11ab0922
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/2099430
Commit-Queue: Stephen Boyd <swboyd@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Stephen Boyd <swboyd@chromium.org>
Auto-Submit: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/hooks/install/qa-elf.sh b/hooks/install/qa-elf.sh
index 750af24..1531d43 100755
--- a/hooks/install/qa-elf.sh
+++ b/hooks/install/qa-elf.sh
@@ -73,7 +73,7 @@
       case "${binary}" in
         *.ko)
           ;;
-        ${D}usr/lib/debug/*)
+        ${D%/}/usr/lib/debug/*)
           ;;
         *)
           check_compiler_flags "${binary}"