Makefile: extract script to massage Shell scripts

Same as in the preceding commits, extract a script that allows us to
unify how we massage shell scripts.

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

generate-script.sh

@@ -0,0 +1,34 @@
+#!/bin/sh
+
+set -e
+
+if test $# -ne 3
+then
+	echo >&2 "USAGE: $0 <INPUT> <OUTPUT> <GIT-BUILD-OPTIONS>"
+	exit 1
+fi
+
+INPUT="$1"
+OUTPUT="$2"
+BUILD_OPTIONS="$3"
+
+. "$BUILD_OPTIONS"
+
+sed -e "1s|#!.*/sh|#!$SHELL_PATH|" \
+    -e "s|@SHELL_PATH@|$SHELL_PATH|" \
+    -e "s|@DIFF@|$DIFF|" \
+    -e "s|@LOCALEDIR@|$LOCALEDIR|g" \
+    -e "s/@USE_GETTEXT_SCHEME@/$USE_GETTEXT_SCHEME/g" \
+    -e "$BROKEN_PATH_FIX" \
+    -e "s|@GITWEBDIR@|$GITWEBDIR|g" \
+    -e "s|@PERL_PATH@|$PERL_PATH|g" \
+    -e "s|@PAGER_ENV@|$PAGER_ENV|g" \
+    "$INPUT" >"$OUTPUT"
+
+case "$(basename "$INPUT")" in
+git-mergetool--lib.sh|git-sh-i18n.sh|git-sh-setup.sh)
+	;;
+*)
+	chmod a+x "$OUTPUT"
+	;;
+esac