Add support for getpagesize

crypto/compat/getpagesize.c

@@ -0,0 +1,18 @@
+/* $OpenBSD$ */
+
+#include <unistd.h>
+
+#ifdef _MSC_VER
+#include <windows.h>
+#endif
+
+int
+getpagesize(void) {
+#ifdef _MSC_VER
+	SYSTEM_INFO system_info;
+	GetSystemInfo(&system_info);
+	return system_info.dwPageSize;
+#else
+	return sysconf(_SC_PAGESIZE);
+#endif
+}