tools: Help magic_check.sh work with other awks

Like the one used by default on Debian Buster. Also, we don't want to
`set -e` by default when we use `false` on purpose...

tools/magic_check.sh

@@ -33,7 +33,6 @@
 # - 0x00112233	(most magic numbers)
 # - 0x00	(where size matters)
 
-set -e
 set -u
 
 ROOT=$(git rev-parse --show-cdup 2>/dev/null) || exit 77
@@ -46,7 +45,7 @@ tr '[:upper:]' '[:lower:]' |
 sort |
 uniq -c |
 sort |
-awk '$1 != 1 || $2 !~ /^0x[[:xdigit:]]*$/ || length($2) !~ /^(4|10)$/' |
+awk '$1 != 1 || $2 !~ /^0x[0-9a-f]*$/ || length($2) !~ /^(4|10)$/' |
 while read -r COUNT MAGIC
 do
 	if [ $COUNT -eq 1 ]