Split logging internals so that platforms may choose additional or alternate spew mechanisms

In the case of windows, allow for the OutputDebugString call in addition to logging to stderr.
Useful for the dll scenario and debugging in Visual Studio.

libnfc/log_posix.c

@@ -0,0 +1,41 @@
+/*-
+ * Copyright (C) 2011 Romain Tartière
+ * Copyright (C) 2011, 2012 Romuald Conty
+ * Copyright (C) 2013 Alex Lian
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser 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 Lesser General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+#include "log.h"
+
+#include <stdlib.h>
+#include <stdint.h>
+#include <inttypes.h>
+#include <stdio.h>
+#include <stdarg.h>
+
+void
+log_vput_internal(const char *format, va_list args)
+{
+  vfprintf(stderr, format, args);
+}
+
+void
+log_put_internal(const char *format, ...)
+{
+  va_list va;
+  va_start(va, format);
+  vfprintf(stderr, format, va);
+  va_end(va);
+}