install hooks: use llvm-readelf

The install hooks use readelf, which is part of binutils. When the
package being built is binutils, this leads to errors like:

/etc/portage/hooks/install/qa-elf.sh: line 13:
x86_64-cros-linux-gnu-readelf: command not found

This change causes qa-elf.sh to use llvm-readelf instead, avoiding
the "command not found" error.

BUG=chromium:1058698
TEST=emerge -e --nodeps cross-x86_64-cros-linux-gnu/binutils; error is gone
R=manojgupta,vapier

Change-Id: Iaad278ecb427dcd329feae87ef3a680b7b1c5e39
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/2095190
Reviewed-by: Manoj Gupta <manojgupta@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Bob Haarman <inglorion@chromium.org>
Commit-Queue: Manoj Gupta <manojgupta@chromium.org>
diff --git a/hooks/install/qa-elf.sh b/hooks/install/qa-elf.sh
index c166bdb..750af24 100755
--- a/hooks/install/qa-elf.sh
+++ b/hooks/install/qa-elf.sh
@@ -66,8 +66,7 @@
     return
   fi
 
-  local CTARGET="${CTARGET:-${CHOST}}"
-  local readelf="${CTARGET}-readelf"
+  local readelf="llvm-readelf"
   local binary
   scanelf -y -B -F '%F' -R "${D}" | \
     while read binary ; do