Minor changes to avoid compiler warnings from gcc in some cases

dlib/assert.h

@@ -82,7 +82,7 @@ namespace dlib
 #  else
 #    define DLIB_FUNCTION_NAME "unknown function" 
 #  endif
-#elif _MSC_VER
+#elif defined(_MSC_VER)
 #define DLIB_FUNCTION_NAME __FUNCSIG__
 #else
 #define DLIB_FUNCTION_NAME "unknown function" 

dlib/logger/logger_kernel_1.h

@@ -603,7 +603,7 @@ namespace dlib
             // following line of code.  However, there is also a bug in gcc-3.3 
             // that causes it to error out if <T> is present.  So this works around
             // this problem.
-#if _MSC_VER == 1400
+#if defined(_MSC_VER) && _MSC_VER == 1400
             hook.set<T>(object, hook_);
 #else
             hook.set(object, hook_);

dlib/uintn.h

@@ -25,10 +25,10 @@ namespace dlib
 #ifdef __GNUC__
     typedef unsigned long long uint64;
     typedef long long int64;
-#elif __BORLANDC__
+#elif defined(__BORLANDC__)
     typedef unsigned __int64 uint64;
     typedef __int64 int64;
-#elif _MSC_VER
+#elif defined(_MSC_VER)
     typedef unsigned __int64 uint64;
     typedef __int64 int64;
 #else