Makefile: extract script to massage Perl scripts

Extract the script to inject various build-time parameters into our Perl
scripts into a standalone script. This is done such that we can reuse it
in other build systems.

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

generate-perl.sh

@@ -0,0 +1,27 @@
+#!/bin/sh
+
+set -e
+
+if test $# -ne 5
+then
+	echo >&2 "USAGE: $0 <GIT_BUILD_OPTIONS> <GIT_VERSION_FILE> <PERL_HEADER> <INPUT> <OUTPUT>"
+	exit 1
+fi
+
+GIT_BUILD_OPTIONS="$1"
+GIT_VERSION_FILE="$2"
+PERL_HEADER="$3"
+INPUT="$4"
+OUTPUT="$5"
+
+. "$GIT_BUILD_OPTIONS"
+. "$GIT_VERSION_FILE"
+
+sed -e '1{' \
+    -e "	s|#!.*perl|#!$PERL_PATH|" \
+    -e "	r $PERL_HEADER" \
+    -e '	G' \
+    -e '}' \
+    -e "s/@GIT_VERSION@/$GIT_VERSION/g" \
+    "$INPUT" >"$OUTPUT"
+chmod a+x "$OUTPUT"