Make Q_ASSUME() an expression (was: statement)

Like Q_ASSERT(), which was fixed for 5.10, it's also useful if
Q_ASSUME() expands to an expression instead of a statement. This way,
it's usable in more contexts, esp. the comma operator.

[ChangeLog][QtCore][QtGlobal] Q_ASSUME() now expands to an expression
(was: statement).

Change-Id: I33dc3d1551a1b7454aa9587b9c33dfa2e3d2b09c
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/global/qcompilerdetection.h

@@ -1132,11 +1132,10 @@
     } while (false)
 
 #define Q_ASSUME(Expr) \
-    do {\
-        const bool valueOfExpression = Expr;\
+    [] (bool valueOfExpression) {\
         Q_ASSERT_X(valueOfExpression, "Q_ASSUME()", "Assumption in Q_ASSUME(\"" #Expr "\") was not correct");\
         Q_ASSUME_IMPL(valueOfExpression);\
-    } while (false)
+    }(Expr)
 
 #if defined(__cplusplus)
 #if __has_cpp_attribute(clang::fallthrough)