QNX: Fix build.

Commit 99357e32a0 introduces a change that
causes <cstddef> to be included instead of <stddef.h> under QNX. That causes
symbols such as size_t to be placed on the std namespace only - QNX does not
put those in the global namespace, since it is not really required by the
standard, and therefore the build fails.

Merry Xmas!

Change-Id: I70c6976203a9d7beadd0076e122e2ac633a4ba69
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/global/qglobal.h

@@ -37,10 +37,10 @@
 
 #ifdef __cplusplus
 #  include <cstddef>
-#else
-#  include <stddef.h>
 #endif
 
+#include <stddef.h>
+
 #define QT_VERSION_STR   "5.5.0"
 /*
    QT_VERSION is (major << 16) + (minor << 8) + patch.