Makefile: refactor generators to be PWD-independent

We have multiple scripts that generate headers from other data. All of
these scripts have the assumption built-in that they are executed in the
current source directory, which makes them a bit unwieldy to use during
out-of-tree builds.

Refactor them to instead take the source directory as well as the output
file as arguments.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

generate-configlist.sh

@@ -1,13 +1,19 @@
 #!/bin/sh
 
-echo "/* Automatically generated by generate-configlist.sh */"
-echo
+SOURCE_DIR="$1"
+OUTPUT="$2"
+
+if test -z "$SOURCE_DIR" || ! test -d "$SOURCE_DIR" || test -z "$OUTPUT"
+then
+	echo >&2 "USAGE: $0 <SOURCE_DIR> <OUTPUT>"
+	exit 1
+fi
 
 print_config_list () {
 	cat <<EOF
 static const char *config_name_list[] = {
 EOF
-	grep -h '^[a-zA-Z].*\..*::$' Documentation/*config.txt Documentation/config/*.txt |
+	grep -h '^[a-zA-Z].*\..*::$' "$SOURCE_DIR"/Documentation/*config.txt "$SOURCE_DIR"/Documentation/config/*.txt |
 	sed '/deprecated/d; s/::$//; s/,  */\n/g' |
 	sort |
 	sed 's/^.*$/	"&",/'
@@ -17,5 +23,9 @@ EOF
 EOF
 }
 
-echo
-print_config_list
+{
+	echo "/* Automatically generated by generate-configlist.sh */"
+	echo
+	echo
+	print_config_list
+} >"$OUTPUT"