Windows: rk_strdup allocator

patchset 3fe5572840 should have
replaced strdup().

Change-Id: I7af7b3e953e379fb23fccd9fa7a9e02c354c2dc4

lib/roken/win32_alloc.c

@@ -33,6 +33,7 @@
 #undef calloc
 #undef malloc
 #undef free
+#undef strdup
 
 /*
  * Windows executables and dlls suffer when memory is
@@ -60,3 +61,9 @@ rk_malloc(size_t size)
 {
     return malloc( size);
 }
+
+ROKEN_LIB_FUNCTION char * ROKEN_LIB_CALL
+rk_strdup(const char *str)
+{
+    return strdup( str);
+}