archive: avoid spawning `gzip`

As we already link to the zlib library, we can perform the compression
without even requiring gzip on the host machine.

Signed-off-by: Rohit Ashiwal <rohit.ashiwal265@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

archive-tar.c

@@ -467,18 +467,34 @@ static int write_tar_filter_archive(const struct archiver *ar,
 	filter.use_shell = 1;
 	filter.in = -1;
 
+	if (!strcmp("gzip -cn", ar->data)) {
+		char outmode[4] = "wb\0";
+
+		if (args->compression_level >= 0 && args->compression_level <= 9)
+			outmode[2] = '0' + args->compression_level;
+
+		gzip = gzdopen(fileno(stdout), outmode);
+		if (!gzip)
+			die(_("Could not gzdopen stdout"));
+	} else {
 		if (start_command(&filter) < 0)
 			die_errno(_("unable to start '%s' filter"), argv[0]);
 		close(1);
 		if (dup2(filter.in, 1) < 0)
 			die_errno(_("unable to redirect descriptor"));
 		close(filter.in);
+	}
 
 	r = write_tar_archive(ar, args);
 
+	if (gzip) {
+		if (gzclose(gzip) != Z_OK)
+			die(_("gzclose failed"));
+	} else {
 		close(1);
 		if (finish_command(&filter) != 0)
 			die(_("'%s' filter reported error"), argv[0]);
+	}
 
 	strbuf_release(&cmd);
 	return r;