Use the NetBSD getopt_long implementation on Windows.

This makes the espeak-ng.c and speak-ng.c source code easier to
read and maintain. It also addresses bugs in command-line argument
parsing with the espeak implementation, for example it treats
`--compile-phonemes` as `--compile` due to an argument matching bug.

src/include/compat/getopt.h

@@ -0,0 +1,49 @@
+/* Compatibility shim for <getopt.h>
+ *
+ * Copyright (C) 2006 to 2013 by Jonathan Duddington
+ * email: jonsd@users.sourceforge.net
+ * Copyright (C) 2016 Reece H. Dunn
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see: <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef GETOPT_H_COMPAT_SHIM
+#define GETOPT_H_COMPAT_SHIM
+
+#if defined(HAVE_GETOPT_H)
+#pragma GCC system_header // Silence "warning: #include_next is a GCC extension"
+#include_next <getopt.h>
+#else
+
+struct option {
+	char *name;
+	int has_arg;
+	int *flag;
+	int val;
+};
+
+extern int optind;
+extern char *optarg;
+
+#define no_argument 0
+#define required_argument 1
+#define optional_argument 2
+
+int
+getopt_long(int nargc, char * const *nargv, const char *options,
+            const struct option *long_options, int *idx);
+
+#endif
+
+#endif