Move the hex digits out of _q_toHex

Avoids them being duplicated several times in QtCore

Change-Id: Idee0168ed9d452a572ad46e2a14d2d4d3c7d2f7e
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

src/corelib/plugin/quuid.cpp

@@ -50,11 +50,11 @@
 #endif
 QT_BEGIN_NAMESPACE
 
+static const char digits[] = "0123456789abcdef";
+
 template <class Char, class Integral>
 void _q_toHex(Char *&dst, Integral value)
 {
-    static const char digits[] = "0123456789abcdef";
-
     value = qToBigEndian(value);
 
     const char* p = reinterpret_cast<const char*>(&value);