Fix setenv/unsetenv link errors by implementing a local version using Windows SetEnvironmentVariable.

Untested, and does not comply with the error returns per setenv.

contrib/win32/nfc_win32.c

@@ -0,0 +1,48 @@
+/*-
+ * Public platform independent Near Field Communication (NFC) library
+ *
+ * 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/>
+ *
+ */
+
+/**
+ * @file nfc_win32.c
+ * @brief Windows System compatibility
+ */
+
+// Handle platform specific includes
+#include "contrib/windows.h"
+
+int setenv(const char *name, const char *value, int overwrite)
+{
+  int exists = GetEnvironmentVariableA(name, NULL, 0);
+  if ((exists && overwrite) || (!exists))
+  {
+    if (!SetEnvironmentVariableA(name, value))
+    {
+      // Set errno here correctly
+      return -1;
+    }
+    return 0;
+  }
+  // Exists and overwrite is 0.
+  return -1;
+}
+
+void unsetenv(const char *name)
+{
+  SetEnvironmentVariableA(name, NULL);
+}