Add uninitialized constructor to qfloat16

Change-Id: Ifc1fa97168927dac96e749b5dcb2a0a38b158b12
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/global/qfloat16.cpp

@@ -72,6 +72,13 @@ QT_BEGIN_NAMESPACE
     \since 5.9
 */
 
+/*!
+    \fn qfloat16::qfloat16(Qt::Initialization)
+    \since 6.1
+
+    Constructs a qfloat16 without initializing the value.
+*/
+
 /*!
     \fn bool qIsInf(qfloat16 f)
     \relates qfloat16

src/corelib/global/qfloat16.h

@@ -43,6 +43,7 @@
 
 #include <QtCore/qglobal.h>
 #include <QtCore/qmetatype.h>
+#include <QtCore/qnamespace.h>
 #include <string.h>
 
 #if defined(QT_COMPILER_SUPPORTS_F16C) && defined(__AVX2__) && !defined(__F16C__)
@@ -76,6 +77,7 @@ class qfloat16
     };
 public:
     constexpr inline qfloat16() noexcept : b16(0) {}
+    explicit qfloat16(Qt::Initialization) noexcept { }
     inline qfloat16(float f) noexcept;
     inline operator float() const noexcept;