config: use chmod() instead of fchmod()

There is no fchmod() on native Windows platforms (MinGW and MSVC), and the
equivalent Win32 API (SetFileInformationByHandle) requires Windows Vista.

Use chmod() instead.
Signed-off-by: NKarsten Blees <blees@dcon.de>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

config.c

@@ -1634,8 +1634,8 @@ int git_config_set_multivar_in_file(const char *config_filename,
 			MAP_PRIVATE, in_fd, 0);
 		close(in_fd);
 
-		if (fchmod(fd, st.st_mode & 07777) < 0) {
-			error("fchmod on %s failed: %s",
+		if (chmod(lock->filename, st.st_mode & 07777) < 0) {
+			error("chmod on %s failed: %s",
 				lock->filename, strerror(errno));
 			ret = CONFIG_NO_WRITE;
 			goto out_free;
@@ -1813,8 +1813,8 @@ int git_config_rename_section_in_file(const char *config_filename,
 
 	fstat(fileno(config_file), &st);
 
-	if (fchmod(out_fd, st.st_mode & 07777) < 0) {
-		ret = error("fchmod on %s failed: %s",
+	if (chmod(lock->filename, st.st_mode & 07777) < 0) {
+		ret = error("chmod on %s failed: %s",
 				lock->filename, strerror(errno));
 		goto out;
 	}