Add implementations for strlcpy/strlcat when missing (#737)

This commit shows how to add implementations of missing functions for
platforms where those functions are not present. In this case we are
adding the `strlcpy()` and `strlcat()`, which are "safe" replacements
for `strncpy()` and `strncat()` that behave in a way more consistent
with developer expectations.

After this commit, adding additional replacements for missing
functions should be fairly straightforward.

[1]: http://stackoverflow.com/questions/3821916/how-to-merge-two-ar-static-libraries-into-one
[2]: https://www.gnu.org/software/automake/manual/html_node/Libtool-Convenience-Libraries.html

include/openthread-windows-config.h

@@ -101,6 +101,11 @@
 // Temporary !!! TODO - Remove this once we figure out the strncpy issue
 #define _CRT_SECURE_NO_WARNINGS
 
+#ifdef OTBUILD
+#include <strlcat/strlcat.h>
+#include <strlcpy/strlcpy.h>
+#endif
+
 // Disable a few warnings that we don't care about
 #pragma warning(disable:4200)  // nonstandard extension used: zero-sized array in struct/union
 #pragma warning(disable:4201)  // nonstandard extension used : nameless struct/union