musl: introduce wrappers for getopt() and getopt_long()

musl's getopt_long() behaves something different in handling optional arguments:
```
$ journalctl _PID=1 _COMM=systemd --since 19:19:01 -n all --follow
Failed to add match 'all': Invalid argument
```
This introduces getopt_long_fix() that reorders the passed arguments to make
getopt_long() provided by musl works as what we expect.

Also, musl's getopt() always behaves POSIXLY_CORRECT mode, and stops parsing
arguments when a non-option string found. Let's always use getopt_long().

src/include/musl/getopt.h

@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+/* getopt() is provided both in getopt.h and unistd.h. Hence, we need to tentatively undefine it. */
+#undef getopt
+
+#include_next <getopt.h>
+
+/* musl's getopt() always behaves POSIXLY_CORRECT mode, and stops parsing arguments when a non-option string
+ * found. Let's always use getopt_long(). */
+int getopt_fix(int argc, char * const *argv, const char *optstring);
+#define getopt(argc, argv, optstring) getopt_fix(argc, argv, optstring)
+
+/* musl's getopt_long() behaves something different in handling optional arguments.
+ * ========
+ * $ journalctl _PID=1 _COMM=systemd --since 19:19:01 -n all --follow
+ * Failed to add match 'all': Invalid argument
+ * ========
+ * Here, we introduce getopt_long_fix() that reorders the passed arguments to make getopt_long() provided by
+ * musl works as what we expect. */
+int getopt_long_fix(
+                int argc,
+                char * const *argv,
+                const char *optstring,
+                const struct option *longopts,
+                int *longindex);
+
+#define getopt_long(argc, argv, optstring, longopts, longindex)         \
+        getopt_long_fix(argc, argv, optstring, longopts, longindex)

src/include/musl/unistd.h

@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+/* getopt() is provided both in getopt.h and unistd.h. Hence, we need to tentatively undefine it. */
+#undef getopt
+
+#include_next <unistd.h>
+
+/* musl's getopt() always behaves POSIXLY_CORRECT mode, and stops parsing arguments when a non-option string
+ * found. Let's always use getopt_long(). */
+int getopt_fix(int argc, char * const *argv, const char *optstring);
+#define getopt(argc, argv, optstring) getopt_fix(argc, argv, optstring)