Docs: fix include header for Qt::*_ordering types

As the classes do not use the common naming pattern, qdoc suggested
some weird non-existend includes when generating the docs for these
classes.
Explicitly use the \inheaderfile qdoc command to point to a proper
include.

Amends bdd41f4.

Pick-to: 6.7
Change-Id: Ia721658df38f1006fdc2fa1de1fab7eb381ceb0b
Reviewed-by: Tatiana Borisova <tatiana.borisova@qt.io>
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

src/corelib/global/qcompare.cpp

@@ -149,6 +149,7 @@ CHECK(strong, equivalent);
 /*!
     \class Qt::strong_ordering
     \inmodule QtCore
+    \inheaderfile QtCompare
     \brief Qt::strong_ordering represents a comparison where equivalent values are
     indistinguishable.
     \sa Qt::weak_ordering, Qt::partial_ordering, {Comparison types overview}
@@ -334,6 +335,7 @@ CHECK(strong, equivalent);
 /*!
     \class Qt::weak_ordering
     \inmodule QtCore
+    \inheaderfile QtCompare
     \brief Qt::weak_ordering represents a comparison where equivalent values are
     still distinguishable.
     \sa Qt::strong_ordering, Qt::partial_ordering, {Comparison types overview}
@@ -484,6 +486,7 @@ CHECK(strong, equivalent);
 /*!
     \class Qt::partial_ordering
     \inmodule QtCore
+    \inheaderfile QtCompare
     \brief Qt::partial_ordering represents the result of a comparison that allows
     for unordered results.
     \sa Qt::strong_ordering, Qt::weak_ordering, {Comparison types overview}