only include .SRCINFO comments in source tarball

This avoids introducing unnecessary changes to the time stamp into
package repositories that regularly use --printsrcinfo to update the
.SRCINFO file.
Signed-off-by: Allan McRae <allan@archlinux.org>

scripts/makepkg.sh.in

@@ -1080,11 +1080,13 @@ srcinfo_write_package() {
 	srcinfo_close_section
 }
 
-write_srcinfo() {
-	local pkg
-
+write_srcinfo_header() {
 	printf "# Generated by makepkg %s\n" "$makepkg_version"
 	printf "# %s\n" "$(LC_ALL=C date -u)"
+}
+
+write_srcinfo_content() {
+	local pkg
 
 	srcinfo_write_global
 
@@ -1093,6 +1095,11 @@ write_srcinfo() {
 	done
 }
 
+write_srcinfo() {
+	write_srcinfo_header
+	write_srcinfo_content
+}
+
 write_pkginfo() {
 	local builddate=$(date -u "+%s")
 	if [[ -n $PACKAGER ]]; then
@@ -2090,7 +2097,7 @@ if (( PACKAGELIST )); then
 fi
 
 if (( PRINTSRCINFO )); then
-	write_srcinfo
+	write_srcinfo_content
 	exit 0
 fi