Merge pull request #560 in FS/freeswitch from…

Merge pull request #560 in FS/freeswitch from ~DDRAGIC/freeswitch:bugfix/FS-8298-gsmopen-libctb-install-error to master

* commit '310ca886':
  FS-8298 fix libctb build

src/mod/endpoints/mod_gsmopen/libctb-0.16/include/ctb-0.16/serportx.h

@@ -13,7 +13,7 @@
 #include <string.h>
 #include "ctb-0.16/iobase.h"
 
-#if _MSC_VER < 1900
+#if defined(_MSC_VER) && _MSC_VER < 1900
 # define snprintf _snprintf
 #endif