Make qt_check_pointer more OOM-safe

First, it can never return, so we can mark it Q_NORETURN and add an
std::termianate at the end. Though if it did, we'd end up in a null-
pointer dereference crash in the caller.

Second, add Q_DECL_NOTHROW to it. It can't throw, but it terminates
execution. This also prevents both puts and fprintf from escaping via
pthread asynchronous cancellation on Linux/glibc.

Third, don't use QMessageLogger, since that allocates memory and
actually uses QString. If we really are in an OOM situation, then
QString's failed allocation would recurse back into qt_check_pointer.
We'd compound the OOM situation with a stack overflow...

Change-Id: Ia53158e207a94bf49489fffd14c81c47971f4e82
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/global/qglobal.cpp

@@ -3016,13 +3016,20 @@ QString QSysInfo::machineHostName()
     If this macro is used outside a function, the behavior is undefined.
  */
 
-/*
-  The Q_CHECK_PTR macro calls this function if an allocation check
-  fails.
+/*!
+    \internal
+    The Q_CHECK_PTR macro calls this function if an allocation check
+    fails.
 */
-void qt_check_pointer(const char *n, int l)
+void qt_check_pointer(const char *n, int l) Q_DECL_NOTHROW
 {
-    QMessageLogger(n, l, nullptr).fatal("Out of memory");
+    // make separate printing calls so that the first one may flush;
+    // the second one could want to allocate memory (fputs prints a
+    // newline and stderr auto-flushes).
+    fputs("Out of memory", stderr);
+    fprintf(stderr, "  in %s, line %d\n", n, l);
+
+    std::terminate();
 }
 
 /*

src/corelib/global/qglobal.h

@@ -753,7 +753,7 @@ template <> class QStaticAssertFailure<true> {};
 #define Q_STATIC_ASSERT_X(Condition, Message) Q_STATIC_ASSERT(Condition)
 #endif
 
-Q_CORE_EXPORT void qt_check_pointer(const char *, int);
+Q_NORETURN Q_CORE_EXPORT void qt_check_pointer(const char *, int) Q_DECL_NOTHROW;
 Q_CORE_EXPORT void qBadAlloc();
 
 #ifdef QT_NO_EXCEPTIONS