lib.sh: add fe_ which is fx_ but err on find

In the mk script, we need fx_ to not return errors on the
find command, since it's searching a bunch of directories
where some of them may not exist.

All other instances where fx_ is used, must return an error
if the directory being searched doesn't exist.

For this, fe_() is introduced, which does the same as fx_
but with this much stricter check.

Signed-off-by: Leah Rowe <leah@libreboot.org>

include/inject.sh

@@ -138,7 +138,7 @@ modify_mac()
 		x_ "$nvm" tmp/gbe setmac "$new_mac"
 	fi
 
-	fx_ newmac "$tmpromdir" -maxdepth 1 -type f -name "*.rom"
+	fe_ newmac "$tmpromdir" -maxdepth 1 -type f -name "*.rom"
 
 	printf "\nGbE NVM written to '%s':\n" "$archive"
 	x_ "$nvm" tmp/gbe dump | grep -v "bytes read from file" || :

include/lib.sh

@@ -128,11 +128,22 @@ setvars()
 	printf "%s\n" "${_setvars% }"
 }
 
+fe_()
+{
+	find_ex "x_" "$@"
+}
+
 fx_()
 {
+	find_ex "" "$@"
+}
+
+find_ex()
+{
+	errx="$1" && shift 1
 	fd="`mktemp`"
 	xx="$1" && shift 1
-	find "$@" | sort > "$fd" || $err "!find $(echo "$@") > \"$fd\""
+	$errx find "$@" | sort > "$fd" || $err "!find $(echo "$@") > \"$fd\""
 	while read -r fx; do
 		"$xx" "$fx" || break; :
 	done < "$fd"